Use it for questions about path aliases, a way of creating pretty human readable URLs to replace system URLs like node/[nid].
Path aliases are alternative paths available for paths defined from modules.
When a path alias is used in Drupal, the content of the original path is shown to the user. For example, if content/node-title-1 is the path alias for node/1, when users visit http://example.com/content/node-title-1, they will see the page for the node with ID equal to 1.
Internally, Drupal will still use the system path and not the path alias.