What are 'cells' in reg tests?

[Peekay Ex]

Hello,

With regard to
http://code.google.com/p/lilypond/issues/detail?id=1858
"unexplained increase in profile reports"

and keith's initial comment:

--snip--

The reported 'cells', in the profile output for the regression tests,
doubled for several tests between 2.15.8 and 2.15.9.

"lyric-tie.profile" was in 2.15.8
 time: 0
 cells: 1125395

and is now in 2.15.9
 time: 0
 cells: 3615166

--snip--

What do these 'cells' indicate and as I do a lot of reg tests now
should I be looking at these more closely than I have been (ie. I
haven't been at all) rather than just focusing on the pretty pictures?

Thanks for your time

--
--
James