The google-site-verification metatag is used to verify page-ownership for Google Admin Console.
Read more about Googles Site Verification at Googles official documentation.
<meta name="google-site-verification" content="QEc1CoW2YiYac-oW8...">
content should be a verification code issued by Google for the Google Admin Console.
In the WHATWG WikiUp to date: v2.3.3