Noun: a fart that occurs when a the farter exerts themselves in a manner usually unassociated with the act of farting itself. Often associated with lifting heavy objects or laughing hysterically. This fart is always unintentional.
Fartee: Help me moves this couch, will ya?
Farter: Sure. *grunts*
Fartee: What? Did you just fart when you picked up your end of the couch?
Farter: Sure did. Couldn't be helped. Action fart.
Fartee: No doubt.