Thanks to GTM, everything becomes much easier – you don’t need to change the source code, you just need to specify in the interface which tags you want to use and when they should be activated.
Tags in Google Tag Manager
A tag in GTM is a JavaScript code fragment that collects data about visitors on a website/application and forwards it to third-party services - Google Analytics, Google AdWords, Facebook, etc.
Google Ads
WIKI: random terms