Proof of Work (PoW) was a fantastic innovation that forms the backbone of the original Bitcoin protocol. The idea is that by solving a computationally intensive math problem, a device can prove the effort it’s done to secure the protocol. The effort that is required to perform these computations contributes to a coin’s scarcity and value.
However, PoW eventually becomes an extraordinarily expensive system. As time passes, the complexity of the problems involved becomes so great that “mining” the last few Bitcoin will require the entire energy output of the sun. Proof of Stake (PoS) solves this issue in a very elegant way. Rather than using computer power as a scarce resource to generate security, PoS uses the scarcity of the coin itself.
A user may “stake” coins to generate the next block in the chain, and the chance of doing so is basically proportional to the “weight” of the staked coins. PoS is eco-friendly, efficient, and avoids the vast waste of energy and hardware overhead of PoW-based networks.