Permalink: definition
A permalink is the final, permanent URL of a WordPress piece of content: a post, a page or, with WooCommerce, a product page.
A structure you choose once, and shouldn't change often
WordPress lets you choose the permalink structure under Settings > Permalinks: a plain URL with a numeric identifier, or a more readable structure including the date or the name (slug) of the content. This setting determines whether a post's address looks like a technical identifier or a readable phrase including the title's keywords.
For a WooCommerce store, the choice of structure has a direct impact on SEO: a structure including the product name is generally more favourable than a purely numeric URL. The real danger comes when this structure changes afterwards on a site already indexed: every existing URL becomes invalid, which breaks links already shared and rankings already earned, unless redirects to the new addresses are put in place.
Frequently asked questions
Which permalink structure should be chosen for a WooCommerce store?
Are permalink and slug the same thing?
Does changing a post's title automatically change its permalink?
Describe your need in one minute
A few targeted questions so I can reply with an estimate rather than another questionnaire.