The phrase "parchment overhang" refers to a situation where a sheet of parchment paper extends beyond the edges of a baking tray or other surface it is placed on. Full definition
Lift bar out of pan using parchment overhang and cut into 16 squares. (epicurious.com)
~ Prepare an 8 × 8» deep baking dish or a 9 × 13» baking dish with foil or parchment and nonstick spray, with some of the foil / parchment overhanging so the treats will be easy to remove. (treatswithatwist.com)
Let sit at room temperature 5 minutes to loosen caramel, then lift from pan with parchment overhang. (bonappetit.com)