What does examination of conscience mean?

It means to look back at what you have done.

Roman Catholic AnswerAn examination of conscience is a "reflection in God's presence on one's state of soul, e.g., in preparation for the sacrament of penance". It is divided into general examen and particular examen. The general examen is "prayerful daily periodic examination of one's conscience to determine what faults have been committed, which call for repentance, and what good actions were performed, for which God should be thanked." The particular examen is a regular examination of one's conscience on a particular moral failing to be overcome or virtue to be exercised. - taken from

Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980

The Catechism recommends that one use the Word of God, particularly the Ten Commandments, the moral catechesis of the Gospels and the apostolic Letters, such as the Sermon on the Mount and the apostolic teachings (Cf. Mt 5-7, Rom 12-15; 1 Cor 12-13; Gal 5; Eph 4-6; etc.)