I'm aware that there are different definitions:

1. One common lay definition is: anything goes.
(not much of a definition, but laymen don't always define words in ways that are useful for scientific purposes)

2. Lacking structure or pattern.

3. Another common def: Being unpredictable.

4. Incapable of being compressed (info theoretic definition).

There are others I might think of, if I took a moment or used google. Anyway, take your pick which definition applies - just tell me which you're using.