A coarse cloth used in making sacks, or bags, such as those for containing grain. It was usually woven from goat’s hair of a dark color. (Re 6:12; Isa 50:3) The Hebrew word for sackcloth (saq) is used also to designate the bags made from it.​—Ge 42:25; Jos 9:4.

It was the traditional garment of mourning, and we first read of its use when Jacob mourned over the supposed death of his son Joseph, girding sackcloth upon his hips. (Ge 37:34; 2Sa 3:31) In some cases the mourners used it as a seat or used it to sleep on. (2Sa 21:10; Isa 58:5; Joe 1:13) The servants of Ben-hadad, in pleading for the life of their king before Ahab, went with sackcloth on their loins and ropes on their heads. (1Ki 20:31, 32) It was worn next to the skin at times, with other clothing on top (Job 16:15; Isa 32:11; 1Ki 21:27; 2Ki 6:30), while in other cases it may possibly have been simply “girded on” over undergarments.​—Eze 7:18; Joe 1:8.

As a result of Jonah’s preaching, the king of Nineveh issued a decree that not only all the people of the city should follow his example of putting on sackcloth but even the ‘domestic animals’ should be covered with it.​—Jon 3:6-8.

The Hebrew prophets were occasionally wearers of sackcloth. They did this in harmony with  the warning messages and calls to repentance they were commissioned to deliver, or when they prayed with expressions of repentance in behalf of the people. (Isa 20:2; Da 9:3; compare Re 11:3.) It was worn by the king and the people in times of great crisis or upon receiving calamitous news.​—2Ki 19:1; Isa 15:3; 22:12.