(Noun). A style of capri-like or long pants made of a loose, light, airy material mainly worn while
lounging around in your
apartment, or at a friend's, but can also be worn out for late-night trips.
Origin: Episode of "Friends"
entitled 'The One With Rachel's Sister". Phoebe refers to Jill's "don't-you-want-to-rent-me-this-apartment? pants" as "apartment pants".