The Church defines a catechism as "a popular summary or compendium of Catholic doctrine about faith and morals and designed for use in Catechesis."
Catechesis is the passing along of Catholic teachings to adults and children. 

As Catholics, we are called to have a knowlege of our faith, and ultimately of our Creator. God has revealed Himself to us fully in the person of Jesus Christ, who desires for us to get to know Him! We get to know "about" Him through study, and we come to know Him personally through prayer and the Sacraments. 

The Catechism of the Catholic Church is a great way to begin to study the faith. There are many Catechisms that have been given to us by the Church over her history. The most recent is linked below.