"BiPAP" is a registered trademark of Philips Respironics for their bilevel machines.
"VPAP" is a registered trademark of Resmed for their bilevel machines.
There are two broad categories of machine, cpap, and bilevel, whereas cpap has one pressure (with some pressure relief) and bilevel, which as different pressures for inhale and exhale.
There are various different types of cpap, (including autocpap, or apap) and many more types of bilevel, from the simple S machine up to highly computerized and automatic machines that monitor and change for every breath.