This is actually a bad example. "The Loop" is a concrete concept within WordPress: it's a global loop (shared across scripts) that represents the portion of the

This is actually a bad example. "The Loop" is a concrete concept within WordPress: it's a global loop (shared across scripts) that represents the portion of the request processing spent looping through the posts that need to get rendered to the page. There are a number of WordPress API calls that only make sense when called from "in the loop", since they rely on global variables that get set in each iteration. Whether or not this is actually a good request handling model is much more debatable, but the comments in your example are meant to communicate that any code which needs to be called from The Loop should get called between them.