PPLNS stands for Pay Per Last (luck) N Shares. This method calculates your payments based on the number of shares you submitted during a shift. The shift system is either time-based or by the number of shares submitted by the miners on the pool. We use PPLNS to prevent the pool-hopping practice and avoid the exploitation of the pool reward system.
When the pool mines a block, the reward system automatically checks up the latest N shares that miners submitted and distributes reward proportionally according to the list.