expression — abbreviation, often Entertainment
an abbreviation for "pay what you can".
Type: 1. Origin — PWYC appears to be Canadian in origin. The term is almost exclusive to Canada (see Chart 1) and the earliest attestations of PWYC appear in Canadian newspapers in reference to theatre performances in Toronto. The term and the practice have spread to other events or services that seek to provide a higher degree of accessibility to patrons (see the 2008 and 2016 quotations).
See also COD-2, s.v. "PWYC", which is marked "esp. Cdn".
Images:

Chart 1: Internet Domain Search, 13 Jun. 2013