title: What are Zombies and what causes them? Are there Zombie processes and Zombie objects?
body: <p>I can find questions about zombies but none that directly addresses what they are and why and how they occur. There are a couple that address what zombie processes are in the context of answering a specific question but don't address the cause.</p>
  
  <p>There are also questions regarding zombie processes and questions about Objective-C/Cocoa-related zombie objects. What are the differences or how are these related? Is an "EXEC_BAD_ACCESS" on Mac/iPhone (or similar error on other platforms) synonymous with a zombie?</p>
  
  <p>How can one <em>prevent</em> zombies and are there any best practices that will help avoid them?</p>
  
  <p>It would be helpful to have this information in one place. This question is intended to be platform/language agnostic, if possible.</p>