Q. 1. What is a "catechumen?"

A. 1. In ecclesiology, a catechumen is one who is being instructed from a catechist in the teaching of the Catholic Church for the purpose of being baptised in the faith.

In no case is a catechumen absolutely bound to be baptized, preserving the principle that the recipient of a Sacrament must not be forced against his will: the person concerned must be drawn spiritually to the faith in addition to being intellectually persuaded.

The Roman Catholic Church revived the catechumenate with its Rite of Christian Initiation for Adults (RCIA) wherein being a catechumen is one of a number of stages leading to receiving the sacraments of initiation (baptism, confirmation, and the Eucharist). This was a result of the Second Vatican Council, explicitly stated in point 64 of the Constitution of the Sacred Liturgy, Sacrosanctum Concilium:

"The catechumenate for adults, comprising several distinct steps, is to be restored and to be taken into use at the discretion of the local ordinary. By this means the time of the catechumenate, which is intended as a period of suitable instruction, may be sanctified by sacred rites to be celebrated at successive intervals of time."

The Neocatechumenal Way and the Light-Life Movement of the Roman Catholic Church take as their inspiration the old catechumenate of early Christianity (the "primitive church") as the basis for their goal of adult faith formation for Roman Catholics.

[Source: https://en.wikipedia.org/wiki/Catechumen]