Google Tag Manager is a tag management system (TMS) offered by Google. It provides a simple platform for managing and updating different types of tags on your website. A tag is a tracking code or snippet of Javascript that sends information about your site to a third party, such as Google. Using Google Tag Manager, you can deploy different types of tracking codes (tags), such as the Google Analytics tracking code on your site without needing to edit your website’s codes. Similarly, you can add codes for event tracking, conversion tracking, remarketing, and more using the Tag Manager.
GTM also lets you test your tags to ensure they are triggered when you load the right page or click a particular button. Another great benefit is that you can change your tags and the way they work without actually changing the source code of your website (which you may not be able to do because of the slow-release cycles or the busy schedule of developers) – instead, you simply edit tags in GTM user interface and publish changes with a click of a button.