Charles Buck Theological Dictionary 
The name of a formulary, or confession of faith, obtruded upon the Protestants, after the death of Luther by the emperor Charles V. when he had defeated their forces. It was so called, because it was only to take place in the interim, till a general council should decide all the points in question between the Protestants and Catholics. The occasion of it was this: The emperor had made choice of three divines, viz. Julius Phlug, bishop of Naumberg; Michael Helding, titular bishop of Sidon; and John Agricola, preacher to the elector of Brandenburgh; who drew up a project, consisting of 26 articles, concerning the points of religion in dispute between the Catholics and Protestants. The controverted points were, the state of Adam before and after his fall; the redemption of mankind by Jesus Christ; the justification of sinners; charity and good works; the confidence we ought to have in God; that our sins are remitted; the church and its true marks, its power, its authority, and ministers; the pope and bishops; the sacraments; the mass; the commemoration of saints; their intercession; and prayers for the dead.
The emperor sent this project to the pope for his approbation, which he refused: whereupon Charles V. published the imperial constitution, called the Interim, wherein he declared, that "it was his will, that all his Catholic dominions should, for the future, inviolably observe the customs, statutes, and ordinances of the universal church; and that those who had separated themselves from it, should either reunite themselves to it, or at least conform to this constitution; and that all should quietly expect the decisions of the general council." This ordinance was published in the diet of Augsburgh, May 15, 1548; but this device neither pleased the pope nor the Protestants: the Lutheran preachers openly declared they would not receive it, alleging that it re-established popery: some chose rather to quit their chairs and livings than to subscribe it; nor would the duke of Saxony receive it. Calvin, and several others wrote against it. On the other side, the emperor was so severe against those who refused to accept it, that he disfranchised the cities of Magedeburg and Constance for their opposition.
Webster's Dictionary 
(1): ( n.) The meantime; time intervening; interval between events, etc.
(2): ( n.) A name given to each of three compromises made by the emperor Charles V. of Germany for the sake of harmonizing the connecting opinions of Protestants and Catholics.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
the name of certain formularies of confessions of faith obtruded upon the Reformers by the emperor Charles V. They were so called because they were only to take place in the interim, till a general council should decide all the points in question between the Protestants and Catholics. There were three of such formularies.
1. THE Interim Of Ratisbon ( Regensburg). Numerous conferences had been held by both parties, i.e. the Romanists and the Protestants, after the formation of the "League of Smalkald" (1531), to bring about a reconciliation. As a literal Roman Catholic writer of our own days (Janus, Pope And Council, p. 369) says, "It was long before men (in Germany and generally on this side of the Alps) grasped the idea of the breach of Church communion becoming permanent. The general feeling was still so far Church-like that a really free council, Independent of papal control, was confidently looked to for at once purifying and uniting the Church, though, of course, views differed as to the conditions of reunion, according to personal position and national sentiment." A conference was finally appointed and held at Worms, under the leadership of Melancthon and Eckius, according to appointment, by Charles V, and afterwards removed to Ratisbon, where the diet met (1541). Here Pflug and Gropper figured prominently by the side of Eckius on the Roman Catholic side, and Bucer and Pistorius by the side of Melancthon. The Roman Catholics now conceded that the communion of both kinds could be administered to all; that the question of sacerdotal celibacy was of no vital importance, etc.; but the Protestants were nevertheless afraid of some hidden plan, and only an apparent reconciliation was effected: it really settled no question at all, satisfied neither party, and finally, as Luther had predicted before the convocation, led only afterwards to much misunderstanding and mutual recrimination. "Let them go on," said Luther, referring to the schemes of those who thought that the differences between Roman Catholics and Protestants might be made up by such conferences, ‘ we shall not envy the success of their labors; they will be the first who could ever convert the devil and reconcile him to Christ … The scepter of the Lord admits of no bending and joining, but must remain straight and unchanged, the rule of faith and practice." Charles V, determined to secure the ratification of the points of agreement entered into at Ratisbon by a national council, forbade the Protestants to argue, in the mean time, on the controverted points, or to dispose in any way of the property of the churches. They protested, however, and went on, regardless of the interim.
2. THE Augsburg Interim After the duke of Alva, through the trechery of Maurice of Saxony, had broken the power of the Progestants at the battle of Muhlberg, and by the overthrow of the Smalkald league, the emperor had brought them helpless at his feet, Charles V, seeing that the pope had not acted in accordance with his wishes at the Council of Trent, decided to attempt by still other conferences to reunite the two cntending parties, or at least "to keep matters quiet until the final verdict of that ecumenical council which constantly vanished in the distance." For that purpose he called the three divines, viz. Julius Pflug, bishup of Naumburg; Michael Helding, titular bishop of Sidon; and the Protestant John Agricola, preacher to the elector of Brandenburg, to agree upon a series of articles concerning the points of religion in dispute between the Catholics and Protestants. The controverted points were, the state of Adam before and after his fall; the redemption of mankind by Jesus Christ; the justification of sinners; charity and good works, the confidence we ought to have in God; that our sins are remitted; the Church and its true marks, its power, its authority, and ministers; the pope and bishops, the sacraments; the mass; the commemoration of saints; their intercession, and prayers for the dead. The result of their discussions was the agreement drawn up in twenty-six articles. These the emperor submitted to the pope for his approbation, and sent copies of them also to the electors of Saxony and of Brandenburg, and to the other evangelical princes. But both the pope and the German theologians refused to adhere to them. The emperor next had them revised by two Dominican monks, who made several alterations, and they were then promulgated as an imperial constitution, called the "Interim," wherein he declared that "it was his will that all his Catholic dominions should, for the future, inviolably observe the customs, statutes, and ordinances of the universal Church; and that those who had separated themselves from it should either reunite themselves to it, or at least conform to this constitution; and that all should quietly expect the decisions of the general council;" and it was published in the diet of Augustburg, May 15, 1548. To the Protestant clergy it granted, for the time being, the right of the matrimonial state, and to the Reformed laity communion of both kinds.
It was truly a standard of faith put forth by the emperor independent of Rome, as the pope refused to sanction it, and in the face of the bitter complaints that came to him that the power and property of the Church should be left in the hands of its present possessors, he showed the pope that he too, like Henry VIII, could regulate the consciences of his subjects, and prescribe their religious faith. The elector of Mentz, quite contrary to the wishes of the other members of the Diet, and of the people there represented, announced the acceptance of the interim by the states, and it was consequently declared law, and printed in Latin and in German. Both Protestants and Catholics began, however, violently to attack it; the Romanists complained of the concessions made to the Protestants, while the Protestant princes (John Frederick of Saxony, the landgrave of Hesse, the margrave John v. K Ü strin, the elector Wolfgang v. Zweibrticken) declined introducing it in their states; the only princes who submitted to it were the elector of Brandenburg, the elector of the Palatinate, the count of Wiirtemberg, and the cities of Augsburg, Halle, etc. (the latter by compulsion).
'''Iii.''' The Leipzig Interim — The Lutheran theologians openly declared they would not receive the Augsburg interim, alleging that it re- established popery: some chose rather to quit their chairs and livings than to subscribe it. Calvin and several others wrote against it. On the other side, the emperor was so severe against those who refused to accept it, that he disfranchised the cities of Magdeburg and Constance for their opposition. Most important, however, for the Protestant cause, and impossible for Charles to pass unheeded, was the opposition against the Augsburg interim by Maurice of Saxony, who denied the right of the elector of Mentz to give himself the approval to an act that demanded the concurrence of the states directly and not indirectly. To fortify himself more strongly in his position, Maurice entered into correspondence with Melancthon, and called a council of state and of prominent theologians at Leipzig and other cities. In the conference at Leipzig it was decided, Sept. 22, 1548, that the Augsburg interim could not be accepted. Yet, for fear of incurring the displeasure of the emperor, a compromise was effected. In a series of resolutions which were adopted, they admitted a great part of the Roman Catholic ceremonials, and tacitly acknowledged also the power of the popes and bishops, but yet well guarded (!) the creed of the Reformers. These resolves of the conference were published as the Leipzig Interim, Dec. 22, 1548.
Subsequently it was divided into a lesser and greater interim. The first was based on resolutions passed at the conference of Celle, and was published by an edict of the elector, and this ultimately became the basis of the greater Leipzig Interim. It was prepared by Melancthon, Eber, Bugenhagen, Major, and prince. George of Anhalt. It restored some Roman Catholic practices; directed that mass should be celebrated with ringing of bells, lighted tapers, and a decorated altar, accompanied by singing, and be performed in Latin by priests in canonicals; that the Hore canoniae and psalms should be sung according to the custom of each place; the old festivals of Mary, etc., were re-established, and meat forbidden on Fridays and fast-days, etc. These decisions, which were promulgated in March, 1549, met with much opposition in Saxony, yet they were strictly enforced, and such ministers as refused to submit to the interim were deposed, as, for instance, Flacius of Wittenberg. The latter then put himself at the head of the opposing party, called by the partisans of the interim Adiaphorists. (See Adaphoric Controversy).
Another treacherous action of Maurice, which secured his services anew to the Reformers, undid all the work already accomplished by Charles V; "and while Henry II was winning, at the expense of the empire, the delusive title of conqueror, Charles found himself reduced to the hard necessity of restoring all that his crooked policy had for so many years been devoted to extorting." In 1552 the Interim was necessarily revoked, and, by the transaction of Passau, August 2,1552, full liberty of conscience secured to all the Lutheran states; and Sept. 21,1555, at the Diet of Augsburg, was finally confirmed the right of the states and cities of the Augsburg Confession (q.v.) "to enjoy the practices of their religion in peace." Compare Menzel, Neue Geschichte, vol. 3; Robertson, Charles V (Harper's edit.), bk. 9:especially p. 377 sq.; and see Bieck, Ueber d. Interim (Leipz. 1727, 8vo); Hirch, Ueb. d. Interim (Lpz. 1753); Baumgarten, Gesch. d. Rel. Partheien, p. 1163 sq.; Schrbckh, Kirchengesch. S. D. Rpf. 1, 592, 674 sq., 683, 686 sq.; Zeitschrift. hist. theol. 1868, p. 3 sq.; Brit. and For. Evang. Review, 1868, p. 631; Lea Hist. of Sacerdotal Celibacy, p. 432 sq.; Hardwick, Reformation (see Ind.); Pierer, Univ. Lex. s.v. (J. H. W.)