What is a slug?
A slug is the piece of the URL that distinguishes a particular page, post or item.
Slugs are effectively there to tell Google what that given page is about. They serve as the defining part of the URL. Google uses slugs as part of its decision-making process when choosing exactly how to rank each page in your website.
In this sense, slugs are very important for SEO. You can choose what the slug is for every item, group, category, deep page, blog and blog post.