The 7 Catholic Sacraments

The traditional definition of a sacrament is this: "A sacrament is a visible sign, instituted by Christ, to give grace." Within this definition there are three important statements:  

A visible sign

An action is performed by a minister (usually a priest). For example, when a baby is baptized in the church the priest pours  water over its head and at the same time says the words "I baptize  you in the name of the Father and of the Son and of the Holy Spirit."  That is a visible sign. 

Instituted by Christ

The Lord Jesus Christ instructed His church to offer the seven  sacraments to His followers. For example, His directive to His  disciples in Matthew's Gospel (28/19), "Go then, to all peoples  everywhere and make them my disciples; baptize them in the name  of the Father, the Son, and the Holy Spirit and teach them to obey  everything I have commanded you." 

To give grace

Grace is God's free gift of Himself as the controlling influence in  our life and the decisions we make once we have committed ourselves  to Him in faith.

In summary, a sacrament is one of the means God has chosen to influence our life in the direction of his purpose for giving us life.