also finishing spray is used to give you that i just got out of the salon....it is an ultra light almost dry mist so it wont ruin a blow dry or someone who had their hair straightened. if you look at the cans some of them say hairspray and finishing spray. I have one from aquanet that really makes my hair gleam.
I've only heard of finishing spray for the face. It's used on after you applied your makeup to keep them fresh and to reduce touch ups through the day.
The main difference is Hairspray is used to keep the hair as a whole in place and finishing spray is used to keep fly aways and bangs under control.