Instantaneous conditional default rate per unit time in a reduced-form credit model: h(t) = lim_Δ t to 0 dfracP(τ in [t, t+Δ t],|,τ > t)Δ t. The survival function is S(t) = P(τ > t) = exp!left(-int_0^t h(s),dsright), and the par CDS spread satisfies the credit triangle s ≈ h,(1 - R) — the standard back-of-envelope for inferring market-implied default intensity from CDS quotes. Constant-hazard (exponential default time) is the bootstrap default; piecewise-constant calibration to a CDS curve is the workhorse.