Unfinished flooring is the chosen raw material, manufactured and cut into its useful form for flooring, and then sold without any finish or protective seal already applied to it.  It usually costs a little bit less for the material itself but will almost always be a more expensive project when installation costs are factored in.  Installation techniques are the same as prefinished wood flooring, but after laying it down and fastening it or floating it for an installation technique, the installer must finish the floor on site, including a sanding process to prep the surface for accepting the chosen finish.  What are the benefits of going with unfinished material and finishing on site?  Some consider it a higher quality installation technique.  It has no seams between planks to worry about; the flooring sits underneath while on top is one, solid coat of protective finish, keeping everything on top of the sealed off wood and not allowing dirt or moisture, however unlikely, to slip down between the boards.  Also relating to the seam lines, unfinished flooring almost always has a square edge on its tongue and groove instead of the microbevel.  This will eliminate seams from appearing in the finish and, depending on the aesthetic of the wood, will sometimes make it appear that your floor is just one solid piece of wood that was cut in the shape of the room(s) it is in.  Choosing your preferred finish is another advantage that finishing on site can provide.  If a more matte finish is desired instead of a typical water-based polyurethane, an installer can apply that after laying down unfinished material.  Along with that, you can change up the tone of unfinished wood with a stain because a finish has yet to be applied; prefinished wood is generally not stained because the prefinishing must be removed.  Unfinished boards acclimate faster than prefinished boards, as well.  However, either material may be sanded, stained (if desired), and refinished after a period of time.

Which one should you choose?  To be honest, we here at SF do not have a preference.  Simply weigh the factors listed above according to which ones are most important to you and compare those aspects against the cost differences given by an installer.  Either one can give beautiful results!