Indexation is when Google references your website on a specific keyword. The indexation must be distinguished from the ranking which takes into account the rank on which you are in a SERP.
Meta Robots and Meta GoogleBot tags forbid the indexation of a page when their value includes Noindex. This HTML tag is located in the <head> of your page.
<meta name="robots" content="noindex">
<meta name="googlebot" content="noindex">
The HTTP X-Robots-Tag header forbid the indexation of the page by search engines when its value includes Noindex. This indication is modifiable in the configuration of your web server.
HTTP/1.1 200 OK
The canonical URL is the preferred URL of your page. If this URL is not valid or corresponds to an URL different from the current URL, the current URL may not be referenced.