VPAID is a specification developed as part of the IAB’s Video Suite; “a set of technical specifications and protocols for in-stream video ad formats that allow compliant ads to seamlessly play across multiple compliant publisher sites.” (http://www.iab.net/vsuite)
Served through VAST, VPAID allows you to run ads with a “rich interactive in-stream ad experience” and to track the details of those interactions.
Read more about VPAID at http://www.iab.net/vpaid.
VPAID in ZEDO
Use the VAST Compatible tab in Create Ad to upload VPAID ads in ZEDO. You can also use the VAST Compatible form to create a VPAID-enabled ad using two non-VPAID, interactive swf files.