XMDP stands for "Media Types for Markup Descriptions of Profiles." That might sound a bit complicated, but it's actually pretty simple.
You know how sometimes you go to a website, and it asks you for information about yourself, like your name and email address? That information is usually stored in something called a profile.
But profiles can be different depending on where you are on the internet. For example, the profile you create on Facebook might be different from the one you create on LinkedIn.
XMDP helps make sure that all these different profiles can talk to each other. It does this by setting some rules for how profiles should be created and shared. This includes rules for things like what kind of information should be included in a profile, and how that information should be formatted.
Think of it like a set of Lego blocks. When you're building with Legos, you need to make sure that all the blocks fit together properly, or else your creation won't work. XMDP is a set of rules that make sure all the different profiles on the internet can fit together properly, like Lego blocks.