According to Wikipedia, a pap Smear is:

In gynecology, the Papanikolaou test or Papanicolaou test (also called Pap smear, Pap test, cervical smear, or smear test) is a medical screening method primarily designed to detect premalignant and malignant processes in the ectocervix. It may also detect infections and abnormalities in the endocervix and endometrium

It's a good idea for women, especially those who are sexually active, to have an annual pap smear. Now there's another reason why pap smears are a good idea. An article in Doc in the Machine talks about a new genetic pap smear:

Undiagnosed sexually transmitted diseases are a major health epidemic in the world. Some of the worst ones have no symptoms. The cervical cancer screening pap smear has been updated with new genetic technology to identify bioth gonorrhea and chlamydia- two of the most serious dangers.

These are hard to detect and may be in the body for years, causing problems and potential danger to sexual partners. With an annual pap smear, you could be sure you're safe.