Casper is proof of stake based consensus algorithm in development primarily for the Ethereum blockchain.
Casper is an implementation of proof of stake consensus algorithm in development for the Ethereum platform. Proof of stake is an alternative consensus method to the proof of work algorithm used commonly in many blockchain projects such as Bitcoin in which block creators are pseudorandomly chosen from a pool of validators based on the amount of coins staked. This is sometimes referred to as virtual mining. Casper is designed to solve the nothing-at-stake problem which occurs in other proof of stake consensus implementations by requiring validators to offer a stake of their coins which can then be slashed under specific protocol conditions whereby the network determines malicious action by that validator.