REP is the token used on Augur, a decentralized prediction market platform. It is an ERC-20 token that runs on the Ethereum blockchain.
The full name of the token is “reputation,” but you will see it abbreviated as REP on cryptocurrency exchanges and in most discussions of the Augur platform.
REP tokens serve two main purposes on the Augur platform. First, if you want to place a bet on the outcome of a given event, you need to use REP tokens. Your tokens are then held in reserve until the outcome of the event is determined. Augur also uses REP tokens to pay winners who bet successfully on a given event using its platform.
Though this is the most common way REP tokens are used, the token is also needed in order to create a market on Augur. If you want to create a market on Augur that would allow Augur users to bet on a particular event, you would have to spend a certain number of REP tokens. You must also stake REP tokens if you want to dispute the reported outcome of an event.