Proof of Stake is a consensus protocol introduced in 2011 as a safer, cheaper, and more energy efficient alternative to the popular Proof of Work protocol. In a Proof of Stake blockchain, the block creator is randomly chosen based on multiple factors (e.g. the amount of cryptocurrency a user owns). There are no rewards for adding a block so the block creator receives a transaction fee.
In a Proof of Stake blockchain, mining is called “forging”