Browser to Web Server to Web Server
When we read pages our browser retrieves them from a web server through an HTML GET. These HTML GETs are our downloads – the bulk of bandwidth and data plans. When a blogger hits the Publish button (input tag) in a WordPress.com site the browser sends an HTML POST to the wordpress.com web server.
<input id="publish" class="button button-primary button-large" type="submit" accesskey="p" value="Publish" name="publish">
Then with a webhook tied to your_server.com, the wordpress.com web server can HTML POST details of your posting to your_server.com. WordPress lets you choose which details to track, and can HTML POST in response to Post Publishing, Page Publishing, and Commenting.
Dashboard(your browser) → WordPress.com(Web Server) → your_server.com(Web Server)
Essentially a WordPress webhook allows you to collect extensive statistics and identity information on your own server. This means you need to have your own server account and some code in your favorite language to listen for HTML POSTs from WordPress.com to the webhooked URL. Such code can save, analyze and display information from any webhooked blog.
A deep coder extra credit opportunity
Robin could ask us to webhook all our blogs to a code on her server for centralized tracking of class publishing and commenting. For comments a great deal of information can be gleaned, but it is not specified that the HTML POST will tell us to which blog a comment is posted. But with a unique URL on Robin’s server for each student blog, we could track the web of commenting relations between students.