What does "white elephant" mean?

An unwanted or useless item, as in The cottage at the lake had become a real white elephant—too run down to sell, yet costly to keep up, or Grandma's ornate silver is a white elephant; no one wants it but it's too valuable to discard. This expression comes from a legendary former Siamese custom whereby an albino elephant, considered sacred, could only be owned by the king. The king would bestow such an animal on a subject with whom he was displeased and wait until the high cost of feeding the animal, which could not be slaughtered, ruined the owner. The story was told in England in the 1600s, and in the 1800s the term began to be used figuratively.