What is EMDR?

I'm recovering (!) from a 28-year marriage with an NPD/Borderline husband. In looking specifically for a therapist accustomed to treating patients with PTSD and/or CPTSD, I've found several. I'm going to talk with one who says part of her work with clients involves EMDR. I looked it up in several spots online, but the end result is that I'm still confused! What do you know about this kind of treatment? Is it legit, or some pie in the sky weirdness? Thanks for your help!!

I found someone who does EMDR also. I'm going to give it a try but I would love to here what Richards take on it is.