What does "nptl" stand for?

[jasoncc comcast net]

What does the .nptl extension on the kernel name stand for?

2.4.22-1.2153.nptl

While we're at it, what does the whole "-1.2153.nptl" mean?

I know the 2.4.22 is major.minor.patch.  I also found an interesting tidbit that I didn't know - I read that all stable versions have an even "minor" number and all development versions have an odd "minor" number.  Found it here - ( http://www.leicester.lug.org.uk/meeting/m000713/Kernel_versions/kernel_versions.html )

-Jason