Update 11/28/2016. this is written before Forge was introduced and some part might be outdated. Please check the latest at forge.autodesk.com. I intend to update when I get a chance.
Autodesk View and Data API is a platform technology that allows the user to upload a model in the Autodesk cloud storage and to view it in a modern Web browser. This is the technology that Autodesk is using internally as well. For example, A360 Collaboration for Revit (C4R) has the viewing capability of a work-shared Revit model on A360. View and Data API is the technology that is used behind the scenes of those features. Although API for C4R itself is not available at this time, Autodesk is making the same technology available to the third party developers to use with their web services applications. View and Data API is current in beta stage.
As this is a platform technology that potentially has an impact to various products, the entire DevTech team has been involved to look at View and Data API in some degree. From my position, I sometimes get an inquiry about difference between Glue viewer and View and Data API viewer, as well as the specific behavior when uploading Revit and Navisworks files. I have also noticed the slight difference in the styles of REST API from Glue web services API.