'Head Covered' in the Bible

And David went up by the ascent of the mount of Olives, and wept as he went up; and he had his head covered, and went barefoot: and all the people that were with him covered every man his head, and they went up, weeping as they went up.

And Mordecai came again to the king's gate. But Haman hasted to his house, mourning and having his head covered.

Every man praying or prophesying, having his head covered, dishonoreth his head.