Catechesis (/ˌkætəˈkiːsɪs/; from Greek: κατήχησις, "instruction by word of mouth", generally "instruction") is basic Christian religious education of children and adults. 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 (quoting John Paul II, Apostolic Exhortation Catechesi tradendae 18):
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.
In the Catholic Church, catechist is a term used of anyone engaged in religious formation and education, from the bishop to lay ecclesial ministers and clergy to volunteers at the local level. The primary catechists for children are their parents or communities. Protestant churches typically have Sunday School classes for educating children in religion, as well as adult classes for continuing education.
–Wikipedia