Drupal 7's HTTP access file, .htaccess, contains some URL rewriting code for redirecting all site visitors to the domain name starting with "www.", in case they try to go to the domain name without the prefix. For instance, you might want all visitors to go to www.example.com, and never example.com, for SEO purposes.
This is achieved by uncommenting the code on lines 81-82:

This guest post was written by Ben Hosmer, a Drupal user new to module development as well as an active member of the Florida Drupal user community. He often blogs about Drupal related topics at radarearth.com

Experienced programmers know the many benefits of using descriptive identifiers, such as the names of variables and functions. Descriptive names make it easier for the original developer — and all who follow — to understand the intent of the code, and to make global changes with minimal risk. In Drupal, when creating a new content type, the site developer assigns a human-readable name (which may consist of alphanumeric characters and spaces) and a computer-readable name (which may consist of lowercase letters, numbers, and underscores).