A family of Microsoft word processing software products for creating web, email, and print documents.
The grey shading may be field shading, you can toggle its display behaviour via File|Options|Advanced>Show Document Content>Field shading.
Knowing that certain content is in a field is useful, because editing it may be a waste of time - most fields revert to their default state when updated by actions such as printing or previewing the document (in general, edits should only be made to the source(s) referenced by a field).