Topic URL's are part of the URL structure used for topics within your website. 

It is a part of search engine optimization (SEO) strategy to create user-friendly and descriptive URLs for topics.

Topic URLs will include the topic name or relevant keywords in the URL path, making it easier for users and search engines to understand the content of the page.

Example:

If you have a Fish News page, previously all filtered versions would simply have had the same URL and page rank.

Now each filtered view (e.g. News/Cod and News/Plaice) will have its own Canonical URL and page rank with far more targeted content. 

This will significantly evolve how search engines index and rank your pages and should lead to improved targeted rankings for all single topic filtered pages.

Please consult the related FAQ: How do I enable Topic URL's?