Peercoin is a digital cryptocurrency similar to Bitcoin and Litecoin. It uses proof of stake technology to prevent the centralization of the network that naturally happens with proof of work coins over time.
Minting (as opposed to mining!) is the term given to Proof-of-stake block generation in Peercoin, that is securing the network. This earns you 1% annual interest. Coins are first eligible to mint 30 days after they have been transferred. If you want to mint, you have to put some of your peercoins at stake in your wallet.
The official peercoin website with a lot of relevant information.