A French term meaning a temporary or secondary place of lodging; a second home. Often used by the sort of person who has a second home in another country and likes to brag a bit.
It literally means "foot to the ground" in French -- from pied ('foot'), à ('to' or 'on'), and terre ('ground').
It is pronounced Pee-ay-duh-TAIR or pyay-dah-TAIR. The plural is pieds-a-terre.