What is a Defi cryptocurrency rug pull?

Could you elaborate on what exactly a "DeFi cryptocurrency rug pull" is? I've heard this term in the crypto community, but I'm not entirely sure of its definition. Is it a type of scam or fraud? How does it typically occur? What should investors be aware of to avoid falling victim to such a pull? Understanding the specifics of this phenomenon would greatly assist in navigating the decentralized finance landscape.