A male prostitute, whose customers are women. Also, by extension, a young man who lives off of an older woman's money.
Of course, that's not how http://www.gigolo.com see it.
From the introduction to the site:
What is a gigolo ?
A gigolo is a man who loves everything about a woman. Of course he is there to care for her body,
but just as important he is there with all his attention. A gigolo is educated, knows about the world,
is independent, is sexually experienced and understands what a woman needs.
Not just sex, but romance, even if it is for just one night, there is connection, passion, fun, humour,
trustworthiness, safety. A gigolo will know how to use his own "tools" and other tools which will
help him achieve his utmost goal: to fully satisfy his lady.