Propagation refers to how the search engine recognizes the changes made on the website. Some of the changes include content updates, technical changes, optimization changes, and more. Search engines recognize the impact made by the new keywords that are added, the new backlinks that are created, and more.
Propagation also helps in redefining how the crawlers and indexers react to the new changes, and this helps in ranking the website higher over time. These modifications and the ability to track these changes help website owners plan their SEO efforts and attract users to their sites.