[throwaway283719]

Meh, it's mathematically deterministic. In reality there is always error (modelling error, measurement error, simulation error) which means that chaotic systems are effectively random on long time scales, even though they are technically deterministic.

[papaf]

I would disagree with the phrase "effectively random" because its too general. Chaotic attractors survive the presence of noise and Chaotic systems look nothing like random data when viewed in a certain way.

Another way of looking at real systems, is that the system is deterministic and the errors are random.