Original: Two guitarists may perform as a guitar tandem, and trade off the lead guitar and rhythm guitar roles. Alternatively, two or more guitarists can share the lead and rhythm roles throughout the show, or both guitarists can play the same role ("dual lead guitars" or "dual rhythm guitars").
Simplified: In some rock or metal bands with two guitarists, the two performers may perform as a "guitar tandem", and trade off the lead guitar and rhythm guitar roles, or both guitarists can play the same role ("dual lead guitars" or "dual rhythm guitars").