In semiotics, linguistics, anthropology, and philosophy of language, indexicality is the phenomenon of a sign pointing to (or indexing) some element in the context in which it occurs. A sign that signifies indexically is called an index or, in philosophy, an indexical.
The modern concept originates in the semiotic theory of Charles Sanders Peirce, in which indexicality is one of the three fundamental sign modalities by which a sign relates to its referent (the others being iconicity and symbolism). Peirce's concept has been adopted and extended by several twentieth-century academic traditions, including those of linguistic pragmatics, linguistic anthropology, and Anglo-American philosophy of language.