Wiktionary
n. (context US English) play put on at theaters during the summer, especially outdoors and during the summer vacation.
WordNet
n. theatrical productions performed by a stock company during the summer
Wikipedia
Summer Stock (UK title: If You Feel Like Singing) is a 1950 Metro-Goldwyn-Mayer musical film. The film was directed by Charles Walters, stars Judy Garland and Gene Kelly, and features Eddie Bracken, Gloria DeHaven, Marjorie Main, and Phil Silvers. Nicholas Castle Sr was the choreographer.
Judy Garland struggled with many personal problems during filming. Summer Stock proved to be her last MGM movie and her last onscreen pairing with Gene Kelly. MGM terminated Garland's contract - by mutual agreement - in September 1950.
Usage examples of "summer stock".
She and her husband, Augustus, were officially retired, but they still found time for the occasional summer stock or dinner theater production, just as Desdemonas parents did.
Too late to get into summer stock now, but there was always winter stock in Florida or Texas or somewhere.
I say the only one because when my mother died, by the time I got back from summer stock to the funeral, there was this closed coffin.
They had come by when he was doing summer stock in Stockbridge after the war.