In digital marketing and web design, a pixel refers to the smallest unit in a digital image or graphic display, representing a single point of color. Pixels are the basic building blocks of all digital images and screens, and their arrangement and color composition create the overall image seen by the user. In online advertising, a pixel also refers to a tiny piece of code placed on a website, which tracks user behavior for analytics and targeted advertising. Understanding pixels is key in creating high-quality digital content, optimizing website design, and effectively executing online advertising campaigns.