A layer 1 is a base blockchain that provides its own security and settlement, such as Bitcoin, Ethereum, or Solana.
L1s compete on throughput, fees, tooling, and decentralization. Apps deploy on L1 or on L2s.
In research workflows, Layer 1 is usually interpreted with Layer 2, TPS, Finality, and Consensus mechanism rather than as a standalone signal. Throughput, finality, and fee markets determine user experience and where activity migrates during congestion.