[CentOS] RHEL Un question

Please excuse my ignorance, since I have not used any RedHat
(enterprise or otherwise) until Fedora FC3 (a few weeks) and now
CentOS4 (permanently). I keep finding references to Un (I believe it's
up to U5 now) in references to bugfixes, etc for RHEL. I presume (?)
these are dot releases after the initial release?

Is there anything equivalent for CentOS, or is this RedHat only behavior?

TIA,

-- 
 Collins
       When I saw the Iraqi people voting three weeks ago, 8 million of them, 
       it was the start of a new Arab world.... The Berlin Wall has fallen. 
               - Lebanese Druze leader Walid Jumblatt