Definition of pre-finished wood flooring

Prefinished hardwood means that it is already finished (w/ stain and Poly) at the manufacturing plant. All you need to do is install it. This contrasts with unfinished hardwood where you install it and then sand, stain and finish it on site.

Installing prefinished is faster since you don't have the extra steps of sanding, staining and waiting for the stain and poly to dry. This can easily add 4-5 days to your project timeline. And, finishing on site is messier.

However, in my area of the country (NY/Northeast), most homeowners prefer the look of when it is finished on site (the floor is smooth vs. microbeveled edges) and it tends to cost a little bit less for unfinished hardwood.

I'm going to attached a link to that better explains the difference.