Yom Kippur is the Hebrew name of the biblical Day of Atonement, one of the “festivals of the Lord” God commanded His people to observe (Leviticus 23:27 Leviticus 23:27Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation to you; and you shall afflict your souls, and offer an offering made by fire to the LORD.
American King James Version×). It’s the second of the festivals that fall during the autumn in the Northern Hemisphere, coming after the Feast of Trumpets.
Atonement is a day of fasting when God commands His people not to eat or drink for the whole 24-hour period.
The Day of Atonement is rich with Christian meaning. It looks forward to the coming time when Satan will be removed as the “god of this world,” and also to the time when all of humankind will begin to live in peace with God as Jesus Christ as the King of Kings and Lord of Lords (2 Corinthians 4:4 2 Corinthians 4:4In whom the god of this world has blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine to them.
American King James Version×, Revelation 20:2-3 Revelation 20:2-3  And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,  And cast him into the bottomless pit, and shut him up, and set a seal on him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.
American King James Version×).
For more information on the Day of Atonement and how it pictures mankind’s reconciliation with God, please read “Atonement: Removal of Sin’s Cause and Reconciliation to God.”