Google AdSense is a program run by Google through which website publishers serve advertisements that are targeted to the site content and audience.
Google Publisher Tag (GPT) is an ad tagging library for Google Ad Manager which is used to dynamically build ad requests.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.