According to Wikipedia: "Abstinence is a self-enforced restraint from indulging in bodily activities that are widely experienced as giving pleasure. Most frequently, the term refers to sexual abstinence, or abstention from alcohol or food. The practice can arise from religious prohibitions and practical considerations. Abstinence may also refer to drugs. For example you can abstain from smoking." 

The most common definition of abstinence refers to staying away from having sexual intercourse, often as a form of contraction so you won't get pregnant.

Obviously, if you do not hav sex and sexual intercourse, if sperm does not enter the vagina,  then you cannot get pregnant. Abstinence is by far the best form of birth control that is available.

Abstinence is a recognized form of birth control, which is defined as any act, drug or device that prevents pregnancy. An act of omission is just as acceptable as a direct act that calls for taking an action.

Abstinence has the added benefit of reducing the odds of catching a sexually transmitted disease as well as protecting your feelings if you are rejected after sex. The pill, diaphragms and injections can work up to 99 percent of the time, but the only way to achieve 100 percent effectiveness is to refrain from intercourse.

Abstinence is the only form of birth control that is 100% effective – in both preventing pregnancies and most sexually transmitted infections. If you choose to be abstinent, then you have decided not to have any type of sexual relations.