An invisible pixel, also known as a tracking pixel or web beacon, is a tiny, transparent image (usually 1x1 pixel) embedded in web pages or emails. While users cannot see it, the pixel allows website owners or attackers to collect information such as when and where content is accessed, user device details, and sometimes even personal data. Invisible pixels are commonly used for legitimate analytics and marketing, but they can also be abused for covert tracking or data theft without user consent.