Unison bends....yeah I do that, now I know what to call it.
Double stops makes sense--and it IS exactly the same as double stops on a fiddle.
A few examples that have caught my ear:
- Robbie Robertsons little Oriental sounding riff in "Shoot Out In Chinatown" on Cahoots. (1st and 2nd strings fingered together gives you that fourth--try it, easy)
- Bruce Cockburn's lazy guitar smooch on "Mama Just wants to Barrelhouse"
- lots of Amos Garrett's playing, such as the famous "Midnight At The Oasis" solo. The master of bending two strings at once--he is something else.