What is a "Browser Message"?

My phone (a Motorola V66i) has separate inboxes for “Text Messages” (normal SMS) and “Browser Messages”

As far as I can make out, they are both actually SMS, and the “Browser Messages” are in PDU format.

Does anyone know what constitutes a “Browser Message”?
How is it distinguished from any other PDU-format SMS message?
What is the format of the content?

Google is turning up stuff about WAP Push, over-the-air provisioning, etc, but it’s rather heavy going! :open_mouth:
Any quick introductory hints, tips, or “beginner’s guide” sites would be most welcome…