What is the 'glass menagerie' in the play The Glass Menagerie? What does it stand for?

The symbol of shattering glass is used in two contrasting yet prominent ways in Williams' script. The first time a glass animal is broken corresponds to the shattering of illusions – Tom's angry speech about where he goes at night, and the Wingfields' first realization that he will inevitably leave them. But when the unicorn breaks, it is in a moment of rare confidence for Laura, as she is dancing with Jim. In that case, the breaking of the glass is a breaking of the shell that holds her in – and the piercing of a hole in her defenses that welcomes a great amount of pain. In the end, Tom reveals in his final recollections that he will forever associate his sister with bits of colored glass behind shop windows – glass hidden (protected?) behind more glass, something too delicate to touch the outside world.