ActiveSync is used to synchronize two devices: typically your desktop (e.g.,
outlook) and your PDA (typically your palm, or other hand-held device).  For
example, I use ActiveSync to synchronize the calendar, contacts, notes, etc.
between my Treo 700 and Outlook.

The "Cradle" is a device many PDAs (but not all) use to connect to the
computer.

-- jesse liberty
Microsoft MVP