The act of self stimulation by stroking, rubbing, or pulling your genitals. Men usually rub, sometimes women will buy dildos or finger themselves. Masturbation can result in ejaculation if the person is stimulated enough. Men/women usually perform this act when intercourse is not an option.
For people with small brains:Masturbation is touching your penis to make it feel good, or for women sticking their fingers in their vaginas.
Guy 1:Sheila is too tired to have sex, and I'm bored.
Guy 2:Why don't you try masturbation?
Guy 1:Isn't that for complete losers?
Guy 2:No dude, it's completely normal and healthy.
Guy 1:I might try it, then.