As far as I'm aware, it's a comparison with how the text is written and how it is presented.
For insance, a newspaper article. It's textual format is article, it's medium of production is newspaper.
Seeing as you're doing conflicting perspectives, I'll assume you're doing Ted Hughes' Birthday Letters. It's textual format is poem, but it's medium of production is anthology. The simultaneous release of his poems creates a different audience response than if they were relased individually.