Coitus Interruptus is the proper name for the ancient birth control method of 'pulling out' or 'withdrawal'.
In this method a penis is removed from a vagina PRIOR to ejaculation. Ejaculate can then be directed elsewhere, largely reducing the risk of insemination.
Coitus Interruptus is not considered a 'safe sex' practice as there is much room for error (in comparison to other contraceptive methods) and it does not protect against STI/STDs.
Further more there is a slight chance of impregnation with pre-ejaculate.