Pool tokens are tokens that are given to Liquidity Providers upon staking which represent their share of the pool’s liquidity and fees.
On Bancor 3, pool tokens represent the pool’s liquidity, which auto-compounds fees and rewards.
Your pool tokens can be staked to earn bonus rewards i.e. rewards paid out in a different token that you've staked and are not auto-compounding e.g. BNT or any third party token your staked token project has chosen to offer.
Bancor 3's pool tokens represent a single-sided stake with no IL downside, meaning they are more stable collateral vs. legacy pool tokens.
The LP tokens are composable ERC-20s that can easily be integrated in other platforms. LP tokens appear in the form of “bnTKN” - e.g., bnBNT, bnLINK, bnUSDC, etc., which will be found in your wallet upon staking.