A catechism is a summary or exposition of doctrine and serves as a learning introduction to the Sacraments traditionally used in catechesis, or Christian religious teaching of children and adult converts. Catechisms are doctrinal manuals – often in the form of questions followed by answers to be memorised – a format that has been used in non-religious or secular contexts as well. According to Norman DeWitt, the early Christians appropriated this practice from the Epicureans, a school whose founder Epicurus had instructed to keep summaries of the teachings for easy learning. The term catechumen refers to the designated recipient of the catechetical work or instruction. In the Catholic Church, catechumens are those who are preparing to receive the Sacrament of Baptism. Traditionally, they would be placed separately during Holy Mass from those who had been baptized, and would be dismissed from the liturgical assembly before the Profession of Faith and General Intercessions.

Catechesis is basic Christian religious education of children and adults, often from a catechism book. It started as education of converts to Christianity, but as the religion became institutionalized, catechesis was used for education of members who had been baptized as infants. As defined in the Catechism of the Catholic Church, paragraph 5 :Catechesis is an education in the faith of children, young people and adults which includes especially the teaching of Christian doctrine imparted, generally speaking, in an organic and systematic way, with a view to initiating the hearers into the fullness of Christian life.