Random

"Governed by chance; not completely determined by other factors. Non-deterministic." (B. S. Everitt (2002): The Cambridge Dictionary of Statistics, Second Edition, Cambridge.)

Note that "random" does not mean either "haphazard" or "without obvious pattern".

In practice, something is only considered "random" when any patterns that exist are either created by a random number generator or indistinguishable from patterns created by a random number generator.