Wiktionary
z-transform
n. (context mathematics English) transform that converts a discrete time-domain signal into a complex frequency-domain representation
Wikipedia
Z-transform
In mathematics and signal processing, the Z-transform converts a discrete-time signal, which is a sequence of real or complex numbers, into a complex frequency domain representation.
It can be considered as a discrete-time equivalent of the Laplace transform. This similarity is explored in the theory of time scale calculus.