Per Chainlink: Most broadly, staking is a cryptoeconomic model that incentivizes the correct behavior of network participants using penalties and rewards in order to strengthen its underlying security
Per Ethereum.org: Staking is a type of consensus mechanism that derives its crypto-economic security from a set of rewards and penalties applied to capital locked by stakers. This incentive structure encourages individual stakers to operate honest validators, punishes those who don’t, and creates an extremely high cost to attack the network.
Per Ethereum.org: Node operators can add a validator to their consensus clients by depositing 32 ETH in the deposit contract. The validator client comes bundled with the consensus client and can be added to a node at any time. The validator handles attestations and block proposals. They enable a node to accrue rewards or lose ETH via penalties or slashing. Running the validator software also makes a node eligible to be selected to propose a new block