Sometimes, the server is not able to fulfil the request (i.e. not return the content
requested), and instead returns a status code which can then be interpreted.
Some common status codes you will encounter in this book include the below.
301: this is used to indicate that the content requested has moved permanently,
and the new version of the content is returned instead. These 301 redirects
are often used in Search Engine Optimisation (SEO) or when a new website is
launched to make sure that old links are redirected to the correct, new content.