Its basically a tool that lets you manage all of the js tracking scripts (tags) that advertisers, affiliates, etc have you paste into a website. So instead of

Its basically a tool that lets you manage all of the js tracking scripts (tags) that advertisers, affiliates, etc have you paste into a website. So instead of having a million js snippets on your page, you have one google tag manager snippet and then your marketing team can inject 400mb of javascript into the site without bothering dev.