Tag:
A tag is a snippet of code that tracks and sends information about activities on your site to third parties (such as Google). You might use tags to track conversions or visits to a particular web page.
In the past, if you wanted to add tags to your site, you'd have to manually add these snippets to the source code of your web pages. This often required going through a developer, which could delay implementation for days or even weeks. And of course, if you needed to make adjustments or updates to the tags, you (or a developer) would need to do so within the page source code.
With Google Tag Manager, you add a single container code snippet to each page of your site. This container snippet handles the deployment and execution of all your tags across the site. You simply add, update and manage the tags you want to use within the Google Tag Manager interface.