it means "A beginner or novice".
It is a term some marine chapters use to rank new members (scouts) in the chapter. The black templars being a big one.
It comes form Latin.
Dark Angels 1750 win/loss Record
Win - 23 (Belial helped wreck Ryan's puny Eldar)
Loss - 13 (Brice's Necrons wiped me)
Draw - 2 (The 13th hold out in alpha take and hold)