What is convex CRV?

Could you please explain what convex CRV is? I've heard it mentioned in the context of cryptocurrency and decentralized finance, but I'm not entirely sure what it entails. Is it a specific type of token, a protocol, or something else entirely? What are its main features and benefits? How does it work within the broader DeFi ecosystem? And finally, how can investors or users get involved with convex CRV?