'Fast' in the Bible

and they mourn, and weep, and fast till the evening, for Saul, and for Jonathan his son, and for the people of Jehovah, and for the house of Israel, because they have fallen by the sword.

and David seeketh God for the youth, and David keepeth a fast, and hath gone in and lodged, and lain on the earth.

and now, he hath died, why is this -- I fast? am I able to bring him back again? I am going unto him, and he doth not turn back unto me.'