(Bird in a) Gilded (Golden) Cage

What does the idiom “(Bird in a) Gilded (Golden) Cage” mean?

Definition:

In a luxurious but confining situation

For example:

“Theresa married a rich guy, but all she does is sit at home and log on to social media. She’s a bird in a gilded cage.”

Notes:

This is from an old American popular song, “Bird in a Gilded Cage.”