the.com/complex number

means A number written as a+bi, combining an ordinary 'real' part with an 'imaginary' part built from i, the square root of -1, letting math handle quantities that plain number lines can't.

from From Latin complexus, 'woven together' (com- 'together' + plectere 'to braid'), since the number plaits a real and an imaginary component into one unit. The 'imaginary' half owes its name to Descartes, who meant it dismissively, doubting such roots were real at all; Euler and Gauss later gave them a respectable home on the complex plane, where 'imaginary' numbers turned out to be just as real-world-useful as any other kind — only sideways.