Google Tag Manager (GTM) is a free tool that allows you to manage and deploy marketing tags (snippets of code or tracking pixels) on your website or mobile app without having to modify the code. This makes it easier to integrate services like Google Analytics, Facebook Pixel, and other third-party APIs. GTM simplifies the process of adding or updating tags, offering a centralized platform to manage them all, thereby speeding up website performance and facilitating collaboration among marketing and IT teams.