if a group of people or organizations "pool" their money, knowledge, or equipment, they share it or put it together so that it can be used for a particular purpose
for instance, you can "pool" money to provide liquidity for trades on the ethereum blockchain via uniswap.
- staking
- automated market makers
- p2p lending/borrowing
E.g. the compound.finance whitepaper explains some technical details well.
One incomplete definition could be that you submit your money temporarily to the control of a mart contract.