Rather than leave you in total suspense, I'm going to just let you know that we are talking about band pull-aparts. There. Now you can rest easy and tune in.
It's very common for people who workout to neglect the posterior muscle groups - the ones that you can't see when admiring your sweet, sweet gainz in the mirror. This is unfortunate because the posterior chain is where we *should* be generating the majority of our power production from. Not just when we lift heavy shit in the gym, but when we take on everyday activities as well. So, let's just say those posterior muscles are important.
To compound the issue, most people greatly overdevelop their anterior muscles - namely the pecs and biceps - which cause some serious dysfunction if not attended to. Band pull-aparts are one of the most simplistic, user-friendly exercises that can be performed often to help turn the tides against anterior overdevelopment and build up that critical posterior.
Below is a quick video on HOW-TO properly perform band pull-aparts. Just like any other exercise out there, doing these with shit form will not produce results and can possibly lead to injury. So let's just agree to check this video out rather than assuming you know your shit based off the name of the exercise.
*NOTE: Let me apologize in advance for neglecting to shoot this video in landscape format. It's been a very long time since I've done a movement lecture/demo video using my phone and I totally spaced how ridiculous it looks when viewed in portrait. I'm sorry, and it won't happen again. Ha!