If you’re wondering what the icon itself signifies, the tipoff comes in the corresponding web address. Here is one we can use as an example:
https://www.google.ca/amp/searchengineland.com/google-url-for-amp-265344/amp?client=safari
Look closely, and you’ll see that even though the link takes us to mobile content from Search Engine Land, it’s actually hosted within Google itself. This is done so the content can be accessed, loaded, and delivered very quickly for mobile users.
The lightning bolt is meant to indicate speed of course. It's no doubt that Google, Facebook, LinkedIn, Twitter and virtually every other major web platform have found that mobile users hate waiting for content to load,use this link for more useful information about these terms mobile accelerated page is the first choice of users and google to help query solutions.