A Layer 1 (L1) blockchain is the base or main blockchain in a particular multi-layer architecture. It maintains its own transaction history and consensus rules.
Layer 1 in context
The label only becomes useful when the relationship is named. In Ethereum’s rollup architecture, Ethereum is the base layer, or L1, for the rollup built in relation to it. The L1 is the underlying chain whose rules and history form the foundation of that arrangement.
“Layer 1” is an architectural description, not a ranking. It does not mean that a blockchain is automatically better, safer, faster or more suitable than another blockchain.
Layer 1 and Layer 2
A Layer 2 system is built in relation to an L1. A rollup is one example of an Ethereum L2 design, but the terms are not interchangeable: L1 identifies the base-chain position, while L2 identifies a system built in relation to that chain.
In short
Layer 1 means the base blockchain in the specific multi-layer system being discussed. The term describes a relationship, not a quality score or an investment category.