an infinite trigonometric series of the form1⁄2a0 + a1 cos x + b1 sin x + a2cos 2 x + b2sin 2 x + …, where a0, a1, b1, a2, b2 … are the Fourier coefficients . It is used, esp in mathematics and physics, to represent or approximate any periodic function by assigning suitable values to the coefficients