Made up bullshit. It's just a word people throw about. Usually by girls referring to their butts as in 'I'm activating my glutes'. Please. Most girls butts are plenty big. I can take my finger - put it on your muscle (lets say your bicep) and get you to concentrate on tensing it while you lift. Even then it's not like the muscle was inactive before.
Warming up is fine (although using light weights still works).
You'd also want the bands on a leg press to pull at the top. And it's not more weight - it's more resistance.
Using bands to activate the muscle group you are about to train allows you to do LESS "warm up sets" while lessening the risk of injury like "warm up sets". I use far less energy activating muscles with bands than I would doing the actual training movements with lighter weight. This allows me to move more weight on my working sets. That is not "bioscience". That is actually a more effective way to prepare for heavy sets