Dead link
A "dead link" is a internet link (otherwise called a 'hyperlink') or URL which no longer directs to anything or directs to something that doesn't exist. For example, the link 'https://creativecommons.org/licenses/by-sa/4.0/' does in fact exist, but https://creativecommons.org/licenses/by-sa/4.0/deed.simple[permanent dead link] does not. Or, for even better example, https://youtube.com/ does exist, however https://youtube.com/what_and_huh[permanent dead link] does not exist.
