Layer 2s or L2s refers to a scaling solution for L1s, whereby transactions are processed on a parallel network by batching user transactions and sending them to the L1. In doing so, a L2 removes congestion from the L1 base layer so it can focus on the security of the network. L2 solutions currently come in the form of Optimistic rollups and Zero-Knowledge rollups. There are other scaling solutions such as Sidechains, Statechannels, Plasma, Subnets etc. This document will only focus on L2 Optimistic Rollups - the initiating developer team deliberately decided to go for a scaling solution with an optimistic approach, as the belief is that this will be the most effective way going forward.