Plain English Meaning
The MFD has many screens. They are sorted into a few simple categories. One knob picks the category, the other knob flips through the screens inside that category.
Full Definition
The organizational structure of the Multi-Function Display (MFD) in a glass-cockpit avionics system, in which related screens are grouped into categories such as Map, Waypoint, Auxiliary, and Nearest. The pilot rotates the outer knob to select a page group and the inner knob to step through individual pages within that group.
Context Anchor
Seen when using a glass-cockpit multifunction display, especially when moving to the nearest-airport pages during instrument flying or training.
Derivation
Page comes from the idea of turning through pages in a book. Group simply means a collection of related pages kept together. The label was chosen because the MFD behaves like a book divided into chapters, with each containing several pages on the same topic.