secret Santa

noun

1. a system whereby each member of a group chooses at random another member of the group for whom to buy a Christmas present at an agreed cost, so that each member buys one present and receives one present
2. a person chosen in this way to buy another person's Christmas present

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012