(idiomatic) A balanced position between two opposite extremes.

plural of happy medium

(informal) A contented, satisfied person or animal.

plural of happy camper

(Australia) Used to express displeasure at someone else's incompetence.

(slang, humorous) An antidepressant.

plural of happy pill

An expression used during Ramadan to wish someone a happy time.

plural of happy-clappy

(music) A genre of rave music typified by a very fast tempo and a bright, cheerful sound, often coupled with solo vocals and sentimental lyrics.