A no-CD crack is a modified executable (.exe on Windows) file. It bypasses the CD checking mechanisms, allowing the user to play without inserting a CD. Commonly used on copied (pirated) games
You might also see the tags NO-CD before a name on Counter-Strike. This indicates the server is running the anti-cheat system, "Cheating-Death", but the user is not running it.
Cheating-Death has been discontinued, and is no longer supported (www.unitedadmins.com)
"Damn, I downloaded that new Hitman game, but it's asking for a CD"
"Hold on, let me send you a no-cd crack"
"OMG WHY DUZ MY NAME SAY NO-CD"
"Because you're not running Cheating-Death"
no cheating death