I know that the title sounds clumsy, but frankly I can't think of any other way to phrase it, and using terms like 'double-stops' sounds too technical.
The idea here is to play a note on the B string, and bend another note on the G string such that both strings hit the same note:
The effect is a stronger sounding note, as demonstrated by the intro to Tell the World above. This method is also used in Planetshaker's Redeemer, do have a look too.
To do this with the E and B strings, play the following:
Lastly, you can use this for soloing, as demonstrated at the end of the video.