Zombie code is code that is neither dead or alive. It is undead!
As frightening as this sounds, this code is being generated every day and the amount of this code is increasing all the time and there are hundreds of millions of lines of this code in existence worldwide.
Zombie code is code that is commented out. It is not alive because it is not runnable. But it is not dead either because it keeps coming back to haunt you! Developers see the zombie code and assume there must be a reason why it exists and leave it. Over time the live code around it changes to the point where the zombie code becomes completely unrelated to the living code.
Zombie code is an iconic amateur practice in software engineering. As a professional it is your duty to kill it whenever you find it.
This blog is named zombie code kill because it is devoted to the art of professsional software development.