A pixel tag is a small, transparent image, usually just one pixel in size, embedded in a webpage or email. It is used to track user behavior and gather data about how visitors interact with content. When a user opens an email or visits a website containing a pixel tag, it sends information back to the server, helping businesses understand user engagement. These tags are often utilized in digital marketing and analytics to measure the effectiveness of campaigns. By collecting data on user actions, such as clicks and conversions, companies can optimize their strategies and improve customer experiences.