What is the circle icon in Chrome's Network tab?

Solution 1:

That's probably a request from a service worker. They reference it as a gear. Cog/gear... What is the difference? Please don't down vote.... I know the difference....

A service worker is a type of web worker. It's essentially a JavaScript file that runs separately from the main browser thread, intercepting network requests, caching or retrieving resources from the cache, and delivering push messages.

Reference from https://developers.google.com/web/ilt/pwa/introduction-to-service-worker

Check out https://developers.google.com/web/fundamentals/primers/service-workers/registration
and https://developers.google.com/web/fundamentals/primers/service-workers