What is a flash loan in crypto?

Could you elaborate on the concept of a "flash loan" in the realm of cryptocurrency? I've heard the term mentioned but am not entirely clear on its mechanics and applications. Specifically, I'm interested in understanding how a flash loan differs from traditional loans, what the key benefits or risks are, and how it functions within decentralized finance (DeFi) protocols. Additionally, I'd like to know if there are any specific platforms or protocols that are known for facilitating flash loans and if they require any specific technical knowledge or setup for users to access.