A continuous vanity is a vanity that crosses the entirety of your master bathroom. It tends to stretch further than a double vanity and also includes a drawer base, wall cabinets, and more between split sinks for increasing bathroom storage along with more access to the things you need!
You could even describe it as an extended double vanity. If you have a lot of things to store in the bathroom, but you don't want to sacrifice square footage for a closet, a continuous vanity could be one of the bathroom storage solutions you need.