2nd guitar; 2nd; in a five piece band there is usually a 'lead guitar' and a 'rhythm guitar'. in some bands the rhythm guitar player is so good he plays many leads or harmonies, he is the '2nd guitar' because he does not simply provide chords for the lead.
protest the hero
fan 1: Luke is definitely the lead and Tim is the rhythm.
PTH fan 2: no way dude Tim is good enough to be a lead himself, he's more of a '2nd guitar' player