Well I know its plainly played on acoustic mostly. It's when you play the bass notes with your thumb and the rest with your other fingers. I'm not sure but just to have some examples, it'd be like well done by passion, or tears in heaven by eric clapton. I don't really understand it yet and i'm pretty sure that when I try to play it, my fingering of the notes are probably the wrong technique. Any thing I could learn about?
Hendrix, frusciante use this alot if you learnt the wind cries mary i'm pretty sure you will have a decent understanding of using it by the time you finished the song.

using that grip frees up your pinky and puts less strain on your tendons, you have to have decent sized hands tho.

basically ur just imitating a regular e shaped barre chord (major, minor, 7ths etc the doors it opens up are great and i love usng this style) you can mute the a string with your thumb.