There are often discussions on trying to edit footage that is in a "delivery format." The topic of GOP comes up. This is an abstract concept, on its surface, especially if one came from a film background, where you could hold your footage up to a light and see each frame.
This ARTICLE covers it pretty well.
Here is a visual example:
You are most welcome. The GOP structure can be an issue, first when editing, if that is the native structure, and also with things like Chapter Point placement, in an authoring program. GOP works fine for compressing larger I-frame files (within parameters), but can really get in the way with frame-accurate editing.