Hybrid POW/POS is a novel approach to distributed consensus mechanisms where both Proof-of-Work and Proof-of-Stake play a role.
Popularized by the well-known cryptocurrency project, Decred (DCR), the overarching purpose of combining the two mechanisms is to balance out the benefits and shortcomings of both.
As an example of the application of such a mixed consensus;
The Proof-Of-Work conducts activities such as mining the next block and serving as general security for the chain, while the Proof-of-Stake helps deal with on-chain politics such as voting.