Charles Sanders Peirce's semiotics is a comprehensive philosophical framework that defines a sign as a triadic relation between the representamen (the form the sign takes), the object (what the sign refers to), and the interpretant (the understanding or meaning generated in the mind of the interpreter). Unlike Ferdinand de Saussure's dyadic model, Peirce emphasized that meaning is not fixed but continuously evolves through interpretation, forming an ongoing process called semiosis. He classified signs into three main categories: icons (which resemble their objects, like a portrait), indexes (which have a direct connection to their objects, like smoke to fire), and symbols (which are based on learned or arbitrary associations, like words). Peirce's model laid the groundwork for much of modern semiotic theory, influencing logic, linguistics, communication studies, and philosophy.