Functional strength is a redundant term. See also:
Spendable money
Edible food
Breathable Oxygen
Wearable clothes
Visible colors
and so on
People have tried to make the point that there is something separate in the concepts of "strength" and "functional strength" for a bit now. It's a fad term as well as being meaningless. What they seem to mean is that if you want to lift a 100 pound bag of potatoes in a barn, you're better off building "functional strength" by lifting potato bags and potato-bag-related items in a barn than training with compound barbell movements in the gym.
Well, that's true to an extent. But training to lift a certain something or to perform any certain action is training, not strength development. There's a reason an Olympic Lifter can dunk a basketball. It's explosive power generated by their strength, which they trained without specificity geared towards dunking a basketball, but guess what? That same strength gives them other abilities.
The interesting thing is this: Strength has a better carryover than training. If I make myself stronger, regardless of how I do it, that increased strength improves my ability level in anything I try to accomplish. There's no activity that isn't improved upon by getting stronger. The converse isn't necessarily true. For example, getting stronger may make someone's golf game improve, but working on golf doesn't necessarily make me a better rower, or bicyclist, or shot putter.
Improving strength makes anyone more functional. Training to do some movement or function improves your ability to perform the function. These terms don't need mixing, nor do all the gains come from specific training (a shot putter training just by throwing or a marathoner just running marathons, etc.).
