What is the RCIA?
The RCIA, which stands for Rite of Christian Initiation of Adults, is a process through which non-baptized men and women enter the Catholic Church. It includes several stages marked by study, prayer and rites at Mass.

What is meant when people refer to men and women 
coming into full communion with the Church?

Coming into full communion with the Catholic Church describes the process for entrance into the Catholic Church for men and women who are baptized Christians but not Roman Catholics. These individuals make a profession of faith but they are not baptized again.

Source: USCCB website