Glossary
Layer 3 (L3)
A rollup that settles to a Layer 2 rather than directly to Ethereum — typically app-specific, with cheaper data and tighter control over execution.
An L3 inherits the same rollup pattern (post data + proof, challenge or validity) but its base layer is a Layer-2 rather than Ethereum. Arbitrum Orbit chains, OP Stack chains that settle to Base, and many ZK Stack chains on top of zkSync are all L3s.
The model produces near-zero gas for end users and full application-level customization (custom gas tokens, sequencer policies, fee discounts). The cost is a longer trust path back to Ethereum, since the L2 sits in between.