A term sometimes used to refer to conmen, due to the stereotype of a slick-looking man in a three piece suit. The term isn't
gender-specific, but most
people seem to use it to indicate a conman (versus the usually more feminine term "grifter").
Three piece also implies that the conman (or woman) was high-class among the stealing trade, or acted and dressed as a
rich person to inspire the confidence necessary to the con.
"I invested my
money, but it turned out my broker was a three
piece."
"I gave that three piece every
penny I had and he stole all of it!"