Newbie Question - what does the "...-p6" mean?

[ograbme]

Hello All.

Thursday, September 14, 2006, 4:24:43 AM, RJ45 wrote in regards to his
message titled "Memory problem":

<snip>

R> I am running FreeBSD 6.1-RELEASE-p6 build with buildworld.

<snip>

What does the "-p6" nomenclature represent in the above statement?
I've noticed some messages have contained various "-pX's".  I recently
just installed FreeBSD 6.1-RELEASE-p0 (according to -uname command)
from a FreeBSD Mall 4-CD set, dated May 2006.  Does this "-p" number
represent an updated ?Version? containing new patches or ...?

Thanks in advance.