The Padre may have another take on this, but the way I see catechumens is that they are being taught the fundamental dogma of the church before they can partake of mass. It's the stage between baptism and confirmation. The thing about the Greek (via Latin) word is that it literally means 'one who is being taught'. Student is literally 'one who is being eager', pupil is literally 'a little boy (pupus)' in Latin (or orphan in French).