Programming term. It's when you take a perfectly good piece of code, change it because you think it's fubar, find out that it's broken now, and blame the person that wrote the original code.
Karl: Look at this code. It's a nelson steamer. Let me change Johnny's screw up.
the next day...
Karl: I found a pretty serious bug today. This is going to take some serious debugging.
Karl: Oh wait. Damn. That's not a nelson steamer. It's a hot karl. The code must've been that way for a reason. Oops.