Many of our folks in the field rely on SharePoint Farm Version number information in Central Administration to compare the patch level between servers. While this number is showing the latest SharePoint Foundation, it doesn’t always mean that you have a completely patched SharePoint farm. The reason, because Microsoft releases many different type of patches:
Cummulative updates (CU) Server packages (Uber packages) Public updates (PU) Stefan Gossner wrote an excellent blog about SharePoint patch terminology and the impact your farm patch level in “SharePoint Patching Demystified” .