From Gmail’s newest features:
Sync your inbox across devices instantly and
automatically. Whether you read or write your email on your phone or on
your desktop, changes you make to Gmail will be seen from anywhere you
access your inbox. Don’t fret if you don’t see "IMAP Access" yet under
the Settings menu. We’re rolling it out to everyone over the next few
days.
If you need a refresher course about IMAP, you can read more about it on Wikipedia.