If you've been investing in the crypto market for some time now, it's likely that you've heard of DeFi. It's a term used to refer to distributed financial protocols and applications (often called "smart contracts"), and these can be found across numerous blockchains like Ethereum and Stellar Lumens. In fact, there are so many different smart contract-based protocols out there that it can be difficult to know where to start with them all! So we're going to take things one step at a time here.
What is DeFi?
DeFi, or decentralized finance, is an umbrella term for financial services on public blockchains, primarily Ethereum. In the context of DeFi, a trading pair refers to a combination of two cryptocurrencies that can be traded against each other in a decentralized exchange.
It aims to democratize finance by replacing legacy, centralized institutions with peer-to-peer relationships that can provide a full spectrum of financial services. 
With DeFi, you can perform various financial activities like earning interest, borrowing, lending, buying insurance, trading derivatives, and trading assets without the need for paperwork or a third party. For instance, trading pairs such as AAVE/USDT play a crucial role in the crypto economy and liquidity, allowing each asset in the pair to be valued without using fiat money.
How Does DeFi Work?
DeFi is a decentralized network of protocols that provide financial services. These protocols are built on top of existing blockchain networks, such as Ethereum or Bitcoin, and allow users to interact with them in new ways.
The main benefit of DeFi is that it makes it easier for developers to build applications around these blockchains. Because they're built using open-source software, anyone can use the codebase if they want--there's no need for permission from any central entity or company (like Google).