[frazell]

ActiveSync was the classic name given to the Sync ability on Windows Mobile. The primary feature was the ability to Sync emails and Contacts with Outlook on the computer.

Exchange-ActiveSync was the extention of ActiveSync on the phone to bypass the computer and sync email and contacts directly with the Exchange server (if supported by the user's email). This name is a misnomer now as Microsoft licenses the protocol used so Exchange is no longer needed for Exchange-ActiveSync. As such, Gmail does support it.

So think of it as Exchange-ActiveSync is the built in way to sync your device's email, contacts, texts, notes, tasks, and calendar with a server over-the-air.