It's funny... After a decade of "pre-built"/"ARF" airplanes, we've forgotten what a kit is. Sig sells its LT-40 in an "ARF" and "Kit" version. Define the differences in these two products and you will define what a "kit" is and what an "AFR" is.

Here is my take on it:
If you don't "glue" anything more on the airplane than the tail and join the wing halves, you're probably holding an AFR.
If you don't "sand" anything beyond the light fitting of the light-ply tank floor, it's probably an ARF.
If you find yourself buying rolls of MonoKote or Ultracote, you've either crashed an AFR or are building a Kit.
If you can fly it in a few days with little or no experience after having been in the hobby for less than six months, it's likely an ARF.
If you have to coat bare wood in the engine compartment to fuel proof it, it's a kit (or bad AFR).
If at any point in construction you're holding a lone, unattached wing rib or fus former, you're probably building a Kit.
If you've been in the hobby 40 years and it still takes two weeks of skilled, dedicated, labor to get it airborne, it's likely a Kit.
If there are 500 of 'em in the world the same exact color, it's likely an ARF. If there are 2 in your club exactly the same, it's probably an AFR.
If you don't feel sightly like crying when it crashes, it's probably an ARF.
If it came in a box 6"x6"x36", it's probably a Kit.
If it came with full size plans, it's probably a Kit.
If the first step in the instructions is to mount the motor mount to the firewall, it's probably not a Kit.
If the fuselage is straight and the wing is not warped, and you don't know how it got that way, it's probably an AFR.
If the fuselage is like a banana and the wing is a DNA double helix, it's not only a kit, it's a kit I likely built.
If the plane is less than 50% light ply, it's likely a Kit.
If when you open the box for the first time, an uniformed bystander can't tell if it's a boat or airplane, it's probably a Kit.
If you when you close the tailgate of the family van on the wing and crush the last three rib bays, your first response is buy another plane, you're probably flying an ARF.
If you cartwheel the plane on landing thereby breaking the fuselage in half and decide it'd be less time consuming to fix it than buy another, it's probably not an ARF.
If the inside of the box smells like plastic covering, it's an ARF. If it smells like fresh cut wood, it's probably a Kit.
If there was less than five things in your cart when you bought it, it's likely you bought an ARF.

Feel free to add. Adjust opinion to taste.

Bill