From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) That part of a human being or quadruped, which extends on either side of the spinal column between the hip bone and the false ribs. In human beings the loins are also called the reins. See Illust. of Beef.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

(usually in the dual, חֲלָצִיַם , Chalatsa'Yim, as the seat of strength, spoken of as the place of the girdle,  Job 38:3;  Job 40:7;  Isaiah 5:27 ["reins," 11:5];  Job 32:1; or as a part of the body generally,  Job 31:20;  Jeremiah 30:6 [so the Chald. plur. חִרְצַין ,  Daniel 5:6]; by euphemism for the generative power,  Genesis 35:11;  1 Kings 8:19;  2 Chronicles 6:9; also מָתְנִיַם , Mothna'Yin, as the seat of strength, Gr. Ὀσφύς , which are the other terms properly so rendered, and refer to that part of the body simply; but כְּסָלַים , Kesalim',  Psalms 38:7, means the Flanks, as elsewhere rendered, prop. the internal muscles of the loins, near the kidneys, to which the fat adheres; while יְרֵכִיַם , put in ( Genesis 46:26;  Exodus 1:5; comp.  Judges 8:30, by euphemism for the seat of generation, properly signifies the Thigh, as elsewhere rendered, being plainly distinguished from the true loin in  Exodus 28:42), the part of the back and side between the hip and the ribs, which, as being, as it were, the pivot of the body, is most sensibly affected by pain or terror ( Deuteronomy 33:11;  Job 40:16;  Psalms 38:7;  Psalms 69:23;  Isaiah 21:3;  Jeremiah 30:6;  Ezekiel 21:6;  Ezekiel 29:7;  Daniel 5:6;  Nahum 2:10). This part of the body was especially girt with sackcloth, in token of mourning ( Genesis 37:34;  1 Kings 20:31-32;  Psalms 66:11;  Isaiah 20:2;  Isaiah 32:11;  Jeremiah 48:37;  Amos 8:10). The term is most frequently used with allusion to the girdle which encompassed this part of the body, i.q. the Waist; especially in the phrase to "gird up the loins," i.e., prepare for vigorous effort, either literally ( 1 Kings 18:46;  2 Kings 4:29;  2 Kings 9:1;  Proverbs 31:17), or oftener as a metaphor borrowed from the loose and flowing dress of Orientals, which requires to be gathered closely at the waist, or even to have the skirts tucked up into the belt before engaging in any exertion or enterprise ( Job 38:3;  Job 40:7;  Jeremiah 1:17;  Luke 12:35;  1 Peter 1:13). (See Girdle).