Lisk uses Delegated Proof of Stake (DPoS) as the consensus system. Delegates generate all of the blocks within the system and these delegates are chosen through a highly competitive election system driven by stakeholders. The number N (currently N = 101) of delegates are chosen to forge by all stakeholders. Each stake holder may vote for up to 101 delegates, and the weight of the vote depends on the amount of Lisk the stake holder possess. A stake holder can vote for a delegate using a vote transaction.
Consensus is a required aspect of any blockchain system. It serves a vital purpose for the system where there are many nodes and all nodes must agree on the integrity of the data. All nodes participating must agree on what transactional data is legitimate in order to move the blockchain forward.
A delegate is a type of account that has registered using a delegate registration transaction, mentioned in section 5.4. These accounts have a special purpose within Lisk as they are allowed to generate blocks for the system provided that the delegate has been allocated enough stake by other users of the system. Any account may become a delegate, but only accounts with the required stake are allowed to generate blocks.
A round within the system is exactly N blocks in length (N is identical to the total forging delegates). During one round, each delegate will forge exactly one block. If an elected delegate cannot forge during a round another delegate will forge their block instead. At the beginning of each round, each delegate is assigned a slot indicating their position in the block generation process. Once a node with an enabled active delegate has forged a block, the node associated with the delegate includes up to 25 transactions into the block, signs it and broadcasts that block to the network. Once the block has reached the network, the next delegate will forge in the slot assigned to them.