Staking in Cosmos refers to the process of participating in the network's proof-of-stake mechanism by locking up a certain amount of the native cryptocurrency, ATOM, to support the security and operations of the network. In return for staking their tokens, participants can earn rewards in the form of additional ATOM coins. Staking plays a crucial role in maintaining the decentralized nature of the Cosmos network and incentivizes token holders to actively participate in network governance and security.