Lisk uses the DPoS which differentiates from i regular PoS (Proof of Stake) as that only the top 101 delegates (determined by voting weight of voters) are actively forging and securing the network.
Lisk DPoS functions through a series of rounds. Rounds consist of 101 individual blocks. Each of the 101 active delegates are randomly assigned 1 block within the round to forge. A full cycle round takes 17 minutes. If a selected delegate is unable to forge their assigned block, activity from that block moves to the next block in the round.