The Google tag (gtag.js) is a single tag you can add to your website to use a variety of Google products and services. Instead of managing multiple tags for different Google product accounts, you can use the Google tag across your entire website and connect the tag to multiple destinations.
The Google tag uses the gtag.js JavaScript library to send data to Google Analytics. In addition to the Google tag, you can use Google Tag Manager to send data to Google Analytics.
The Google tag was previously referred to as the global site tag.
The analytics.js JavaScript library is no longer supported by Google Analytics.