These are two individuals, usually a male and a female, who occasionally engage in noncoital sexual behavior (most often masturbation but possibly other forms) without being lovers or having any long-term commitment. Usually this is done on an infrequent basis if one or the other is in need. Think of this as one possible and occasional outcome of a strong friendship between a man and a woman. I hope this definition does not offend.
While Tom and Jennifer's relationship was usually Platonic, sometimes theirs devolved into that of 'friends with minor benefits.'
"Friends With Minor Benefits" denotes a relationship in which two friends participate in non-coital activities usually designated for more intimate relationships without the attached emotional bond.
These activities can range anywhere from simple making out all the way to mutual masturbation and/or oral sex, but does not include actual coitus (that would be considered "friends with benefits").
Guy: I walked in on Bob and Mary in a heated makeout session earlier.
Girl: I didn't know Bob and Mary were going out?
Guy: They're not. They're just friends with minor benefits.