Unison bends are played on two strings. In the example below, we strike both notes at the same time and bend the note on the note on the 7th fret until it comes in unison (has the same pitch) as the note on the 5th fret.
This is called a unison bend.
When performing them, be sure to listen for the 2 notes to “come together” in unison. A common mistake is under-bending and overbending the string. This will make it sound like it’s out of tune. A unison bend requires you to bend the string so that both notes sound at the same pitch.