In the poker glossary, the chip leader is the person having the largest number of chips out of all players left in a tournament. The term can also be used in other contexts, including cash games, but it most often applies to multi-table tournaments.
For example, there are 50 players left in a tournament, and two players with large stacks play a big pot. One of them wins and suddenly finds himself sitting with 5,000,000 in chips. Nobody else left in a tournament has that big of a stack, so announcers may say something to the effect of “We now have a new chip leader.”
A chip leader is not an official title of any kind, and due to the nature of tournaments, the position of a chip leader tends to change quite frequently.
