The practice of restraining oneself from indulging in sex.
Here sexual abstinence refers to the decision to forgo all forms of penetrative sex, masturbation, and orgasm in general.
People who chose to practice sexual abstinence can do so for any number of reasons, including semen retention, recovery from porn addiction, religious beliefs, birth control, a depressive emotional state, or difficulty in finding a partner.
Likewise, the duration of abstinence can very, from a set period of time, e.g. 30 days, or long-term.