conversation piece

1. An unusual object that arouses comment or interest.
2. A genre painting, popular especially in the 18th century, depicting a group of fashionable people.

An unusual object that arouses comment or interest, as in That bust of Aunt Nettie is ugly but it's an excellent conversation piece. In the early 1700s this same term was used for a particular kind of painting that represented a group, often a family, arranged as though they were conversing with one another. Later in the century the term was extended to any object that stimulates conversation.

The noun has one meaning:

Meaning #1: something interesting that stimulates conversation