A catechumen can also refer to one who is preparing for chrismation (or confirmation) to be received from a heterodox Christian communion.
It is interesting that some Eastern Orthodox Churches make a practise of referring to Christians that seek instruction and Chrismation using the ancient moniker of the unbaptized.
Just interesting is all.
Most Roman Catholic parishes require baptized and practising Christians to undgo a year long process that parallels the catechumenate alongside catechumens.