CRV is the governance token of Compound, a decentralized finance (DeFi) protocol. When CRV was frozen on Aave (Matic), it meant that users were unable to transfer or trade the CRV token on the Matic Network. This was due to a security vulnerability in the Matic Network, which was discovered and reported by the Compound team. To protect user funds, the Compound team took the precautionary measure of freezing the CRV token on the Matic Network until the vulnerability was fixed. The vulnerability has since been fixed, and the CRV token is now unfrozen on the Matic Network.