What does a status of "P" mean during a Tortoise CVS Update operation?

It's equivalent to a 'U', but CVS figured that sending a patch rather than the whole updated file would be smaller.

I couldn't quickly find a fuller explanation, but here's a table of codes.

According to various sources, P refers to a file patched individually rather than updated (U).

See http://www.gjt.org/mlist/jcvs/msg01480.html and a bunch of others except I'm a new user so I can only post one link :-( for details.

I couldn't find any docs specifically for Tortoise CVS that explained this though.

P stands for patch. It means only a small update was made, so the whole file did not need to be sent.