A slug is a few words that describe a post or a page.
Example: When a user is looking to increase their overall site traffic, they will customize their individual slugs to contain precise keywords to increase search engine optimization.
About the Word
Slugs are used in the permalink structure and are created by default in WordPress. If you do not choose to define the slug, it will be automatically generated using the title of the page or post, separating each word using hyphens. While the auto-generated permalink may contain some key words, WordPress has given the user the ability to set the slug to contain the most optimized key words.
You can edit the slug when you are editing a page or post as seen in the highlighted area below.