what is POI?

The algorithm rewards people not for being wealthy, but for supporting the network - you are rewarded according to your importance. PoI is the beating egalitarian heart of NEM. This Proof-of-Importance (POI) is qualitatively different from both Proof-of-Work and Proof-of-Stake.

Proof of Importance (PoI) is a novel method for security distributed peer-to-peer (P2P) currencies, using the structure of the transaction graph to determine nodes that are structurally important to the overall network. PoI is closely related to Proof of Stake (PoS), where holding units of currency for a period of time gives a person a higher "stake" in the network.