Chillout, lounge and downtempo describe electronic music slowed below dance tempo and arranged to sit in the background. The format was defined by the chill-out rooms of nineties clubs and has since become the default soundtrack of hotel lobbies, which is both its strength and its reputation problem.
For practical purposes this is one of the most useful categories in the directory. Chillout channels have consistent level, no vocal hooks competing for attention, and rotations deep enough to run for a full working day without obvious repetition. Where instrumental classical is too dynamic and ambient is too static, chillout sits in between.
It is also gentle on bandwidth. The genre is synthetic, mid-tempo and without the sharp transients or sub-bass that cause trouble at low bitrates, so a 64 or 96 kbps chillout stream is genuinely acceptable rather than a compromise. If you are looking for something to leave running all day on a metered connection, this category is the place to start.