Charles Buck Theological Dictionary 
A kind of regulation for the performance of religious worship, drawn up by the assembly of divines in England, at the instance of the parliament, in 1644. It was designed to supply the place of the Liturgy, or Book of Common Prayer, the use of which they had abolished. It consisted of some general heads, which were to be managed and filled up at discretion; for it prescribed no form of prayer, or circumstances of external worship, nor obliged the people to any responses, excepting Amen. The substance of it is as follows:
It forbids all salutations and civil ceremony in the churches;
the reading the scriptures in the congregation is declared to be part of the pastoral office;
all the canonical books of the old and New Testament (but not of the Apocrypha) are to be publicly read in the vulgar tongue: how large a portion is to be read at once, is left to the minister, who has likewise the liberty of expounding, when he judges it necessary. It prescribes heads for the prayer before sermon; it delivers rules for preaching the word; the introduction to the text must be short and clear, drawn from the words or context, or some parallel place of Scripture. In dividing the text, the minister is to regard the order of the matter more than that of the words: he is not to burden the memory of his audience with too many divisions, nor perplex their understanding with logical phrases and terms of arts: he is not to start unnecessary objections; and he is to be very sparing in citations from ecclesiastical or other human writers, ancient or modern, &c.
The Directory recommends the use of the Lord's Prayer, as the most perfect model of devotion; it forbids private or lay persons to administer baptism, and enjoins it to be performed in the face of the congregation; it orders the communion-table at the Lord's supper to be so placed, that the communicant may sit about it. It also orders, that the sabbath be kept with the greatest strictness, both publicly and privately; that marriage be solemnized by a lawful minister of the word, who is to give counsel to, and pray for the parties; that the sick be visited by the minister under whose charge they are; the dead to be buried without any prayers or religious ceremonies; that days of fasting are to be observed when the judgments of God are abroad, or when some important blessings are desired; that days of thanksgiving for mercies received be also observed; and, lastly, that singing of Psalms together in the congregation is the duty of Christians. In an appendix to this Directory it is ordered, that all festivals, vulgarly called holy days, are to be abolished; that no day is to be kept but the Lord's day; and that as no place is capable of any holiness under pretence of consecration, so neither is it subject to pollution by any superstition formerly used; and therefore it is held requisite, that the places of public worship now used should still be continued and employed. Should the reader be desirous of perusing this Directory at large, he may find it at the end of Neale's History of the Puritans.
Webster's Dictionary 
(1): ( n.) Direction; guide.
(2): ( n.) A collection or body of directions, rules, or ordinances; esp., a book of directions for the conduct of worship; as, the Directory used by the nonconformists instead of the Prayer Book.
(3): ( n.) A book containing the names and residences of the inhabitants of any place, or of classes of them; an address book; as, a business directory.
(4): ( n.) A body of directors; board of management; especially, a committee which held executive power in France under the first republic.
(5): ( a.) Containing directions; enjoining; instructing; directorial.
Watson's Biblical & Theological Dictionary 
an ecclesiastical instrument containing directions for the conduct of religious worship, drawn up by the assembly of divines, by order of parliament, in 1645. It was intended to supply the use of the Common Prayer Book, which had been abolished. It orders the reverent observation of public worship, prayer, singing of psalms, the reading and exposition of the Scriptures, &c. It enjoins no forms, but recommends the Lord's prayer as a model of devotion; directs that the Lord's Supper may be received sitting; that the Sabbath day be strictly observed; but puts down all saints' days, consecrations of churches, and private or lay baptisms. This Directory, which was formerly bound with the Westminster confession of faith, is still, in effect, the plan of worship among the Dissenters, and especially the Presbyterians.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
I. a set of rules for worship and ordination, drawn up to take the place of the Liturgy, or Book of Common Prayer, by the Westminster. Assembly of Divines. The Directory was framed in 1643, ratified by Parliament January 3, 1644, and adopted by the Scottish General Assembly in 1645. In the Act of 1844, it is entitled a Directory for the Public Worship of God throughout the three Kingdoms of England, Scotland, and Ireland. The same ordinance repealed the acts of Edward VI and Elizabeth, by which the Liturgy was established, and forbade the use of it within any church, chapel, or place of public worship in England or Wales, appointing the use of the Directory in its stead. This ordinance, indeed, never received the royal assent, and it was a long time before it succeeded in abolishing the established worship. In some parts the Directory could not be procured, in others it was rejected; some ministers would not read any form, others read one of their own. The Parliament, therefore, in the ensuing summer, called in all the Books of Common Prayer, and imposed a fine upon such ministers as should read any other form than that imposed by the Directory. The penalty for reading the Liturgy was 5 for the first offense, 10 for the second, and a year's imprisonment for the third; for non-observance of the Directory, 40s. Any one who should preach, write, or print anything in derogation of the Directory was to forfeit not less than 5, nor more than 50, to the poor. All Common Prayer-books remaining in parish churches or chapels were ordered to be carried to the committee of the several counties within a month, there to be disposed of as the Parliament should direct (Rushworth, Hist. Coll. page 4, 1:295, cited in Eadie, Ecclesiastes Cyclopaedia s.v.).
The Directory prescribes no form of prayer, nor any responses on the part of the people, except Amen. It enjoins that "the people shall enter the churches reverently, and in a grave and becoming manner, without adoration, or bowing towards one place or another; that the minister is to begin with prayer; to which all present are to give due attention, and to abstain from all private conferences or salutations; that the reading of the Scriptures in the congregation, which is a part of the worship of God, be performed by the pastors and teachers; that all the canonical books of the Old and New Testament, but none of those called apocryphal, be publicly read in the vulgar tongue, and in the best allowed translation; that the portion to be read at once be left to the minister, but that commonly one chapter of each Testament be read at every meeting; that all the canonical books be read over in order, that the people may be the better acquainted with the Scriptures; that when the minister shall judge it necessary to expound any part of what is read, he is not to begin his exposition till the whole chapter or psalm be ended, and that after reading the Scripture and singing the psalm, the minister who preaches is to begin with prayer.
It then prescribes heads for the prayer; enjoins that the subject of the sermon be a text of Scripture, which teaches some principle or head of religion, or is otherwise suitable to the occasion; and recommends that the introduction to the text be brief and perspicuous, and drawn from the words or context, or from some parallel passage of Scripture. In dividing the text, the minister is to regard the order of the matter rather than that of the words; he is not to burden the memory of his hearers with too many divisions, nor perplex their understandings with logical phrases and terms of art; he is chiefly to insist on those doctrines which are principally intended, and most likely to edify his hearers; he is not to propose nor answer any unnecessary objections, but to confute error, and satisfy the judgments of his audience; and he is to be very sparing in quotations from ecclesiastical or other human writers, ancient or modern, etc. The Directory recommends the use of the Lord's Prayer as a perfect model of devotion. It forbids private or lay persons to administer baptism, and enjoins it to be performed in the face of the congregation. It orders that the communion-table at the Lord's Supper be so conveniently placed that the communicants may sit about it. It enjoins that the Sabbath be observed with the greatest strictness, both in public and private; that marriage be solemnized by a lawful minister of the word, who is to give counsel to, and pray for the parties; that the minister teach the people not only in public, but in private; that the sick be visited by the minister, under whose charge they are, and who shall administer spiritual good to their souls; that the dead be buried without any prayers or religious ceremonies; that days of fasting be observed when the judgments of God are abroad in the world, or when some important blessings are desired; that days of thanksgiving for mercies received be also kept; and, lastly, that as it is the duty of Christians to praise God publicly, the whole congregation join together in singing psalms. In an Appendix it is enjoined that all festivals, vulgarly called holy days, be abolished, and that no day be observed except the Lord's day; and that, as no place is capable of any holiness under pretense of consecration, or subject to pollution by any superstition formerly employed, the places of worship now used be still continued."
This Directory, which is still partly, but by no means strictly, adhered to by Presbyterians in the British Islands, is given in full in Neal, History of the Puritans, appendix 8; see also Collier, Church History of England, 8:287 sq.
II. The Presbyterian Church in the United States has a Directory for Worship, in fifteen chapters, which was amended and ratified by the General Assembly in 1821, and may be found appended to The Constitution of the Presbyterian Church (Philadelphia, Presbyterian Board).
III. In the Roman Catholic Church an annual Directory (Directoriumn) for the clergy is published, which gives rules of ceremonial according to the calendar for the year, as settled by the bishop of the diocese. The Ritualists in England have imitated this in their so-called Directorium Anglicanum.