Difference between "friendly" and "official"

In a sentence or two, or kindly share a link as well if this has already been addressed (I’ll keep searching)… what is the functional impact between two teams going against one another in a Friendly match vs. an Official match? I hope that makes sense, I mean logically it’s straightforward, but before I go ahead and try testing each out, I was wondering from a code/functional standpoint, what does the theme ‘do’ as a consequence of selecting each?

Thanks!