Google canbus and look at the Wikipedia site. A decent description in there.
The Wiki definition is, unsurprisingly, written by a systems nerd and consequently completely misses the engineering benefit that drew carmakers to CAN BUS in the first place - and that is the fact that the wiring loom can be a multi-component serial loop carrying both power and data signals. The traditional loom was individual "there and back" pairs to every individual component, resulting in kms of wiring and kgs of weight in complicated cars. Not good for cost, weight (and therefore emissions). The geeky stuff about letting your wipers talk to your brakes was a tertiary benefit that came later on.
