Coitus interruptus is a Latin term meaning interrupted intercourse. It is the clinical term for the withdrawal method of contraception, which is when a male withdraws his penis from his female partner prior to ejaculating. It is sometimes referred to as "being careful".
It is true that doctors, nurses, and sexual health educators have not, in the past, talked much about withdrawal method. It is not a very effective form of birth control, and it does not protect against any STDs, so the inclination has been to focus on better, more effective types of contraception and STD prevention. However, it is likely that withdrawal is actually the most commonly used form of birth control, and for that reason sexual health professionals have begun, slowly, to talk about it more.
Does it work? It does work, some of the time. The generally regarded failure rate for withdrawal is 19 percent, meaning if 100 women used withdrawal as their only method of birth control for one year, 19 of them would get pregnant. Keep in mind though that statistics on withdrawal are only as good as the method and people who report them.
The two main disadvantages to withdrawal are that it does not protect from STDs, including HIV, and the failure rate is very high compared to other methods. One of the reasons for this is that prior to ejaculating, a small amount of pre-ejaculate (also called pre-cum) will come out of the penis. There is sperm in pre-ejaculate, and it is possible that this could cause a pregnancy.
There is no question that withdrawal is not a very good form of birth control, and it is not safer sex at all. But it might be considered better than nothing.