1.VerbTo stimulate oneself sexually, especially by use of one’s hand or a sex toy made for this purpose, often to the point of ejaculation or orgasm.
"I'm looking for some hot videos to masturbate to."
2.VerbTo manually or by other means than one's own genitals stimulate someone else's genitals sexually.
3.VerbTo stimulate or please oneself by means of anything, not necessarily sexual, that does not get them anywhere; something that wastes their time; something that does not help others or achieve any important goal.