What does "gilded cage" mean?

The encumbrances or limitations that often accompany material wealth, as in She had furs, jewelry, whatever money could buy, but was trapped in a gilded cage. This metaphoric expression indicating that riches cannot buy happiness was popularized (and possibly coined) in a song, “A Bird in a Gilded Cage” (1990; lyrics by Arthur J. Lamb, music by Harry von Tilzer), about a young girl marrying for wealth instead of love and paying for luxury with a life of regret.