First, what is DEFI?
DeFi, short for decentralized finance - it's the notion that crypto entrepreneurs can recreate traditional financial instruments in a decentralized architecture, outside of companies' and governments' control. Compound is a crypto version of a money market fund, letting users earn interest.
Basically, DEFI Staking allows you to invest your existing Crypto and earn interest from it. There are several staking platforms out there and you must do your own research before investing in one of them. Remember only invest what you are comfortable in losing.