Here is the MECA (Model Engine Collector's Association) guide to describing engines:

New In Box (NIB) Unused and in the original factory supplied carton, complete with all accessories as supplied by the factory which may include coil, condenser, lead wire, wrench, instructions and parts lists and matching serial number on box.

New (N) Unused and complete with all parts as originally sold by the manufacturer. No marks on mounting lugs.

Like New (LN) Run a few times, slight marks on the mounting lugs, otherwise as new.

Excellent (EXC) Run a few times, slight marks on the mounting lugs, slight discoloration of cylinder, cylinder head or other parts due to heat. Very slight scratches on the engine, good compression. Light wear on bearing surfaces.

Very Good (VG) As excellent, but used more with very good compression, slightly enlarged mounting lug holes, one or two deep scratches, or moderately discolored spots, small chipped or bent cylinder fins, bearing surfaces discernibly worn.

Good (G) As very good, but compression and bearing surface wear sufficient to warrant this rating. This rating considered the minimum internal condition necessary for use as a runner type engine.

Fair (F) Compression sufficient to run, but with reduced power output. Bearing surfaces well worn one or more missing or badly chipped, bent, scratched or repaired parts. One or more open mounting lugs. Unacceptable as a display engine, but possibly capable of a G or VG rating if overhauled and or replacement parts added.

Parts (P) A parts engine. Worn out, poor compression, broken or missing parts, surfaces badly scarred. Will not run in present condition. Not suitable for use or display.

Cosmetic (C) Engine should not be run due to weakened or deteriorated parts but cosmetically able to be classified at a higher rating.

David