The word functional has been used in medicine to describe a condition symptomatically identical to another. Eg functional hypoglycemia is hypoglycemia symptoms without actual blood sugar drop.

There are two reasons it’s used

1) it’s easier to type (*)

2) Placate people who are strongly convinced it’s the same thing. To them “functional” means “nearly the same but not yet understood”. For others it’s just a way to sidestep the first group and have a conversation.

When I see a world like this consider the intended audience. When you and I talk, we drop the word because we both know we’re are talking about (*) “this system is exhibiting goal-seeking behavior similar to other systems that are understood to pursue goals”. If I don’t know the person I will use the word and focus on the subject.