The term 'slug' which is used in Django comes from the world of newspaper editing:-
So this name is an informal name that is given to a story during the production process. As the story winds its tortuous path from beat reporter through to editor through to the "printing presses", this is the name it is referenced by, e.g., "Have you fixed those errors in the 'Russia-cuts-Europe-gas' story?".
So Django uses “slug” as part of the URL to locate the story, an example being:-