A handjob, as referred to in the popular song "Moondance" by Irish singer Van Morrison. The original line from the song was "Well it's a marvelous night for a handjob" but the record company forced Van Morrison to change it.
Man - "How about a moondance?"
Woman - "Hold on, I need to wash my hands."
to have sex outside at night
its a wonderful night for a moondance.