ODST is short for Orbital Drop Shock Troopers, it was a division in the UNSC army that was sent into suicidal battles. It is purely voluntary, and only the "bravest" would join. Their motto is, "Jump feet first into hell", since they droped down in pods that got extremely hot. Their journey from space to earth was very rough, and sometimes a few would die, either from the heat or the impact. They look hella badass, and are in all halo games. They wore black suits, and had combat knifes. they are in all "Halo" games, and they kickass XD. In Halo 3 they are even able to complete almost an entire mission on their own. Don't underestimate them. They were nicknamed the "Helljumpers".