There is no better way to describe the RCIA, a familiar process in our parishes, than by quoting the Catechism of the Catholic Church:
§1229: “From the time of the apostles, becoming a Christian has been accomplished by a journey and initiation in several stages. This journey can be covered rapidly or slowly, but certain essential elements will always have to be present: proclamation of the Word, acceptance of the Gospel entailing conversion, profession of faith, Baptism itself, the outpouring of the Holy Spirit, and admission to Eucharistic communion.”
§1233: “The Second Vatican Council restored for the Latin Church ‘the catechumenate for adults, comprising several distinct steps.’ The rites for these stages are to be found in the Rite of Christian Initiation of Adults (RCIA).”
While the initials RCIA actually stand for the liturgical celebrations which mark the steps of the catechumenate, common usage has led to the initials designating the whole process of the catechumenate but also, generally, the journey in faith taken by baptized Christians who seek to become Catholics or baptized Catholics who have never completed their initiation.