Proof of Participation from what I understand is a new unique consensus algorithm used in ZooBC , which has been mentioned before "a protocol that measuring which nodes are actually participating in the peer-to-peer network, and gradually remove the nodes from the federation which are not participating. "
You can learn more about it here.
But what is the "consensus algorithm"?
Consensus algorithm is like an agreement of "truth" since blockchain itself is a decentralized system that means there is no central authority to maintain the system. So to create a safe transaction among people without any central power, there must be one objective truth we called protocols or consensus algorithms.
Here, the protocols/consensus algorithms replacing human referees in a given network. Click to know more
Hope it's helpful!