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One who is exploring whether to become Catholic is known as an Inquirer and is in the stage known as Period of Evangelization and Precatechumenate, as explained by the USCCB's webpage devoted to explaining the Rite of Christian Initiation of Adults. It goes on:
After a conversation with a priest, or RCIA director, the person, known as an "inquirer," may seek acceptance into the Order of Catechumens, through the Rite of Acceptance. During this Rite, the inquirer stands amidst the parish community and states that he or she wants to become a baptized member of the Catholic Church. The parish assembly affirms this desire and the inquirer becomes a "catechumen."
Those who are already baptized Christians desiring full communion with the Catholic Church, known as Candidates, go through a process known as formation. As practical matter at many parishes, both candidates and catechumens attend many (if not most) of the same instructional classes.