freebsd version numbers

[Pieter Donche]

I upgraded to Freebsd systems from 7.0 to 7.2
on the first one, done May 25th, I use the generic kernel
$ uname -a reports: 7.2-RELEASE #0

on the second one, done 3 days later (May 28th)
on this system I also build and installed a custom kernel after upgrade.
$ uname -a reports:  7.2-RELEASE #1

Why is this different? (#0 versus #1)

What does #Number actually mean: is this the same as -pNumber used in
the mails from   @daily          root    freebsd-update cron
"The following files will be updated as part of updating to X.Y-RELEASE-pNumber"

If not, what is the difference ?

what's the difference between version, level, patchlevel, 
'release level', 'version level of a release' (any others ?), ...