An infinite series in which an analytic function f (z ) defined on an annulus about the point z₀ may be expanded, with nth term a_n(z-z₀)ⁿ, n ranging from -∞ to ∞, and a_n = 1/(2π i ) times the integral of f (t )/ (t - z₀)ⁿ⁺¹ along a simple closed curve interior to the annulus. Also known as Laurent series.