Lambda (λ) — ir-fuel ratio (normalised)

Lambda is the air-fuel ratio normalised by the stoichiometric AFR for the fuel. λ=1 means stoichiometric. λ<1 means rich (more fuel). λ>1 means lean.

Lambda is what wideband O2 sensors report. Tuners read lambda to set fueling on Stage 2/3 builds. Typical WOT target on petrol turbo: λ 0.80-0.85 (rich for knock margin).