A slug is a translation of a page title into a form suitable for a URL.
For example, `include-another-pages-roster-in-your-own` is the slug for Include Another Page's Roster in Your Own.
**Explanation**
Consider a lineup that includes Include Another Page's Roster in Your Own. That text includes two characters that are not allowed in URLs: a space and an apostrophe.
If you check the browser's address bar when visiting that page, you'll see that the URL there contains this text:
> https://.../include-another-pages-roster-in-your-own/...
The title has been transformed by changing a space into a dash and just removing the apostrophe.
For the most part, you won't care about slugs. But certain plugins require you to type in the slug rather than the page title. See Add a Roster for an example.