A service provided by Google that helps website owners control tags on their sites without requiring a development team to maintain them. Tags are generally snippets of code that can be used to track user behavior, ad performance and other marketing efforts. These tags can be provided by 3rd party services like Facebook ads or they can be custom developed to suit a site owner’s needs. Enabling GTM usually involves dropping a small code block onto a site. Once that happens, tags can be created and deployed from GTM without the need of updating the site’s codebase.