Gill spacing can be a useful character in determining a mushroom's identity, but it does have the drawback that we don't have a term for "normal", or "average".
The gill spacing shown here, for instance, is probably the most usual that you will see (also in store-bought mushrooms, for example); it is considered crowded, or close.
Of course, none of this has really been standardized. " Close", in particular, has been used in different publications to mean what I call crowded, what I call subdistant, or to mean something in between. While it has an "obvious" natural meaning, I try not to use it (it may slip out a few times during the course of the web site), as I find it just ambiguous, unless specially defined: for example, Lincoff(1987) gives explicit pictures of only three states: crowded, close, and distant. He may very well have the right idea.