What is a sentence using the word discrete?

A relation that is defined for each element in its domain and for each input there is one and only one output.

A discrete function is either equivalent to infinite sequences (if aperiodic) or to finite sequences, n-tuples (if periodic). In engineering language, it is the same as the term "sampled function".

References: Fischer, J.V. On the Duality of Discrete and Periodic Functions. Mathematics 2015, 3, 299-318.