Δ = dfracpartial Vpartial S — the share-equivalent hedge ratio. For a BSM call Δ_call = N(d_1) in (0,1); for a put Δ_put = N(d_1) - 1 in (-1,0). Approximately equal to the risk-neutral ITM probability for ATM options (delta-as-probability heuristic on the FX desk). Quoting convention varies by market: equities quote in dollars, FX in 'delta strikes' (25-delta risk reversal, 25-delta butterfly), rates in DV01.