What makes a good slug
Google's guidance on URL structure comes down to a few rules:
- Readable words instead of long ID numbers.
- Hyphens between words. Google says they help people and search engines pick out each word, and advises against the underscore (_).
- Words in the language your readers search in. Google's own examples include German and Chinese URLs.
- One spelling: URLs are case sensitive, so /Shoes and /shoes are different pages to Google.
Slug or permalink?
In WordPress the permalink is the full, permanent address of a post, and the slug is the post's own part of it. WordPress builds the slug from the title: its documentation gives "This Is A Great Post!" becoming this-is-a-great-post. The permalink settings choose what goes around it, such as the date or a category.
Editing the slug of a live page
Changing a slug changes the URL, so the old address stops working unless something redirects it. Google recommends a permanent server-side redirect when a URL changes. Some platforms add that redirect for you and some don't, so open the old URL after the change and check where it lands.