BEP-20 is a token standard on Binance Smart Chain that extends ERC-20, the most common Ethereum token standard. You can think of it as a blueprint for tokens that defines how they can be spent, who can spend them, and other rules for their usage. Some common BEP-20 Tokens are: Binance-Peg BUSD Token (BUSD), Wrapped BNB (WBNB), etc.
For more information about BEP-20 Token, visit https://academy.binance.com/en/glossary/bep-20.