DeFi is an exciting new space of decentralized finance. Usually trustless and non-custodial.
DeFi is rapidly expanding and allowing for new use-cases and ideas to be realized. Automated Market Making, Decentralized Exchanges, Flash Loans, Lending, Sushi Farming. etc.
The DeFi space is going to be one to watch in the 202x's.
Most DeFi is done on smart contract based chains such as Ethereum (ETH) as it has the best developer tooling and a flexible scripting language. But many DeFi products don't require all of this power - which also bring high fees.
As DeFi expands new DeFi focused blockchains will be appearing, and exising blockchains will have DeFi products added to them, or supported via sidechains(SmartBCH on Bitcoin Cash)
* All terms and definitions may update as the Cryptionary improves.