Google Tag Manager (GTM) is a user-friendly tag management system by Google, designed to simplify the process of deploying and managing tags, triggers, and tracking codes on websites and mobile apps. It allows marketers and webmasters to add, update, and monitor tags through an intuitive interface without needing to modify site code manually. GTM's system of triggers and variables ensures precise tag firing based on specific conditions, enhancing flexibility and accuracy in tracking and analytics implementations.