Masturbation is the act of manually stimulating the genitals so as to achieve sexual pleasure, sexual arousal, and/or orgasm. Most often, masturbation is done by a person to himself or herself, but it is also possible to masturbate another person.
A person who masturbates is called a masturbator, a female is called masturbatrix.
Masturbation in childhood
Boys masturbate more than girls, and the ability to reach orgasm increases with age. By the age of 5, about 50% of boys have had an orgasm, according to a study from the 1970s. This figure rises to about 80% by the age of 13 and nearly 100% by the age of 15. Before puberty, orgasms are normally "dry", without an ejaculation of semen. During and after puberty, there are also so-called wet dreams (nocturnal emissions) which are ejaculations of semen during sleep. These are usually not due to manual stimulation and therefore not cases of masturbation.
Statistically, girls masturbate less and reach orgasm less often than boys. Only about 25% of 15-year-old girls have experienced an orgasm. Girls, too, can have nocturnal orgasms, but this occurs less often too.
Historically, some centuries ago it was common in Europe for parents, nurses and nannies to calm young children by playing with their genitals. This was not seen as masturbation: the children were so young that sexual thoughts were far from the mind. Today, such practice is socially unacceptable and illegal by law, as it constitutes child sexual abuse.
Masturbation and spanking
At one time masturbation was commonly regarded as sinful or unhealthy or both; sometimes referred to as self-abuse. Therefore, children were punished when detected in masturbation, not infrequently with a spanking. Sometimes a wet dream aftermath might be interpreted as such evidence.
Nowadays the unhealthy concept is falling to the wayside with a general neutrality being prevalent, with hints there might even be health (physical and psychological) benefits.
In some BDSM relationships, one partner (most often the submissive partner) may be forbidden from masturbating, or from doing so in the absence of the other partner, or from doing so without permission. Violations of such agreements may be reasons for spankings or other punishments. The ban can also be enforced with the help of a chastity belt.
Spankophiles also often enjoy masturbating while (or after) reading spanking stories, viewing spanking art, or watching spanking videos, if they find such media sexually arousing. Many spankophiles enjoy masturbating immediately after being spanked (or after spanking) or even during spanking.
(Male) masturbation is colloquially called spanking one's monkey.