From Longman Dictionary of Contemporary English in action someone or something that is in action is doing the job or activity they are trained or designed to do photos of ski jumpers in action see/watch something/somebody in action I’d like to see the new computer system in action. → action Examples from the Corpus in action • It's a chance for students to see a court in action.

the process of being active; energetic activity; effect or influence: a man of action