The "Golden Age of Hollywood" refers to the period of time when the American commercial film industry was completely contained within the "studio system," which started to form during the '20s, but hit it's full stride by the '30s, and completely disappeared by the end of the '60s.

During this time, a small number studios would not only finance and produce the films, but had control of actors and directors via extensive contracts, and exclusive rights to distribute their films to whatever theaters they wanted. So if your theater wanted to get the hot new Cary Grant picture, you'll have to also take a bunch of inferior b-pictures from the same studio.

This infrastructure started to crumble after the US Supreme Court enacted an anti-trust ruling against Paramount Pictures in 1948, which forbade the vertical integration that built the studio system. As studios began to lose control, the film industry shifted away from the almost mass production style model, to a more director-oriented one in the late '60s-early '70s (Scorsese, Coppola, Spielberg, etc.), at which point the Golden Age was officially dead, and "New Hollywood" took over.

The Golden Age also had a distinct aesthetic tone, and uniformly wholesome content, as the same accepted period of the Golden Age/Studio System coincides almost exactly with the acceptance of the "Hayes Code," an informal agreement setting standards for moral decorum in film, forbidding sexual, graphically violent, and drug related content, along with things like blasphemy and miscegenation. Internationally, and prior to the Hayes Code, there are examples of much racier content than can be found in Golden Age Hollywood, though clearly not to the extent of modern film.

So not only was there a clearly defined economic framework that identifies the "Golden Age," but also one grounded in the content and attitudes.