Think of a URL slug as the fingerprint of a web page. It's that unique part of the web address that comes after your domain name. If you look at "grocktool.com/tools/slug-generator", the "slug-generator" bit is what we're talking about here.
Back in the early web days, URLs looked like technical gibberish—"page.php?id=473&cat=2". They meant something to servers but nothing to humans. Today, slugs tell both users and search engines what to expect on a page before they even click. When you see "best-coffee-shops-seattle", you instantly know what you're getting.
Good vs. Bad Slug Examples:
A well-crafted slug does three important things: it tells search engines exactly what your page is about (helping with rankings), gives users confidence they're clicking the right link, and makes your content easier to share. People are more likely to remember and type "yourbrand.com/contact" than "yourbrand.com/index.php?page=contact-us-form". It's one of those small details that makes your site feel professional and trustworthy.