title: custom commands / keyword in command prompt
body: <p>This has to be a very simple question... but as long as i can remember i've seen special keywords or commands in the windows command prompt which are clearly not system commands like dir cd etc</p>
  
  <p>Today i was reminded of this using node.js and from the command prompt I cd'd into a director and typed "npm install".</p>
  
  <p>My question is simple... how does the keyword/command "NPM" get associated with a corresponding exe or other "command handler"?  I would think this is very basic but after searching through the internet, its surprisingly hard to find the explanation.</p>
  
  <p>E.g. how could i associate "stack /overflow" with some kind of process/exe that would be able to parse out the "overflow" variable.</p>