QB that plays well enough to earn a high paying second contract.
QB that a majority of NFL praises as elite.
QB who often times has to carry or will his team to TDs.
QB who is respected by his team mates and by his peers.
QB who has had success at every level.
and mostly, a QB who is the face of your franchise (i.e. Franchise QB).
Blake Bortles was a franchise QB. LOL
I will take Corrosion's description of what a franchise QB is.
A QB that wins big games. (Big games happen in the playoffs).
A QB who produces when it matters most.