A baby xenomorph, shown in the entire Alien serious as well as Alien vs Predator 1 and 2. This is the 2nd stage in the xenomorph development after a human (or something of comparable size) is attacked by a face-hugger. After a short period of incubation it burst out of a hosts' chest like an evil bloody penis, then runs of somewhere to feed and grow at an unnaturally fast rate.
A chest-burster is the last thing the hosts sees before they die.
by Rena Snake March 04, 2008