Meantone

I'm new to Meantone, so please bear with me. The discussion was:

>}Pitch Alteration from EQ [1/64 of a semitone]
>}C 0
>}C# -15
>}D -4
>}D# +7
>}E -9
>}F +2
>}F# -13
>}G -2
>}G# -17
>}A -7
>}A# 4
>}B -11
>
>}Any comments?
>
>This looks like 1/4-comma meantone from Eb to G#. That's probably a good
>default for what "Meantone" means without any further information.

My ignorant question: what does "1/4 comma" mean? What's a comma?

Second question: I notice that the tuning above has the "in tune" fourths
tuned to 502 cents. I'm tuning a pedal steel with the fourths at 503 cents.
I really like it. What should I call this temperament?

http://wco.com/~quasar/tunings/fscale12.htm

-b0b-

>Why don't you just use a regular steel guitar? A steel manufacturer named
>"Cougar" specializes in long necked, non-pedaled instruments.

Perhaps I ought to let her (my mom, by the way) reply, but I think the
answer is that it sounded like fun to to build one for herself!