Watch the Double Stop Bends online guitar lesson by Chris Buono from 60 Electric Guitar Techniques You MUST Know
Much like unison bends, you're playing two different notes at the same time on adjacent strings, but this time the bent note is not intended to match the pitch of the note on the higher string, instead it's meant to become a minor third (more often) or major second (less often) interval among other intervals. It's a phrasing tool that comes ripping through the mix every single time.
Looking for inspiration? The shriek of double stop bends immediately makes me think of the SG-wielding Angus Young. That's his jam and I thank him for it.