Meaning: Deep mourning or repentance.
Esther 4:1
When Mordecai perceived all that was done, Mordecai rent his clothes, and put on sackcloth with ashes, and went out into the midst of the city, and cried with a loud and a bitter cry;
Jeremiah 6:26
O daughter of my people, gird thee with sackcloth, and wallow thyself in ashes: make thee mourning, as for an only son, most bitter lamentation: for the spoiler shall suddenly come upon us.
Daniel 9:3
And I set my face unto the Lord God, to seek by prayer and supplications, with fasting, and sackcloth, and ashes: