AFI Token is issued to users of the protocol who stake the LP tokens issued for supplying liquidity on pairs on Uniswap or Balancer or who stake afiTokens.
afiTokens
When depositing stable coins in the farming pools, users receive a receipt ERC20 token corresponding to the particular stable coin. Deposit DAI to get afiDAI, deposit USDT to get afiUSDT.
When you withdraw from the pool you are effectively depositing your afiTokens back in to the pool to claim your yield.