Decentralized finance (DeFi) is the internet, for money. It uses blockchain technology, which enables trustless transactions between two entities, so you don’t need to go through a trusted middleman, like a bank, an exchange or a securities broker.
This is made possible by cryptography, so you trust transparent, sophisticated mathematics rather than a human being to do the right thing with your money. It is vastly more efficient than antiquated financial architecture, in the same way your smart phone is more efficient than an old fixed-line phone. The end result is that the middleman is cut out, so you earn more. Your money works harder for you in DeFi than in the traditional system.