404
The 404.twig view renders the page a visitor is taken to if they enter an invalid URL.
Considerations
When the visitor is presented with a 404 error page it should be made clear to them that the page they were looking for could not be found.
Furthermore it's a good idea to present the user with instructions on what to do next, consider the following:
i) Including a search bar
ii) Including a link to the home page of your website