Shrove Tuesday gets its name from the ritual of shriving that Christians used to undergo in the past. In shriving, a person confesses their sins and receives absolution for them. When a person receives absolution for their sins, they are forgiven for them and released from the guilt and pain that they have caused them. In the Catholic or Orthodox context, the absolution is pronounced by a priest. This tradition is very old. Over 1000 years ago a monk wrote in the Anglo-Saxon Ecclesiastical Institutes:

In the week immediately before Lent everyone shall go to his confessor and confess his deeds and the confessor shall so shrive him.
So, there ya go!