Semiotics is the academic field dedicated to the study of signs. A sign (for example, the word "ship") may be recognized by the presence of its constituent parts, which in semiotic theories based on Saussure's, at least, are the signifier (the container, or the sign's perceptible form: the letters s-h-i-p) and the signified (the meaning or content; the notion conveyed by the signifier: 'a vessel of considerable size for deepwater navigation'). With these concepts, general semiotics allows us to describe any system of signs: texts, images, performances, multimedia productions, traffic signals, fashion, daily life, etc. There are specific semiotic systems (for text, images, multimedia, and so on) that take into account the specifics of each system of signs. This chapter is an overview of general semiotics. In the first section, we define the field of semiotics and the concept of the sign, and enumerate the basic concepts and the names of some of the better-known theorists. Then, by analysing a seemingly innocuous object, the traffic signal, we illustrate some concepts of general semiotics – notions such as sender/receiver, sending/transmitting/receiving, channel, context, referent, system, code, redundancy, noise, paradigm/syntagm, margin of safety, seme, isotopy, polysemy/homonymy/synonymy, symbolic/semi-symbolic/semiotic relationships and systems, arbitrary/conventional signs, contiguous/noncontiguous signs, single/repeated signs, successive/simultaneous signs, actualized/virtualized signs, contrast, and so forth.

A system of signs or a relationship between elements of any kind is symbolic, semi-symbolic, or semiotic (the word "semiotic" has a restricted, specific meaning in this context). When one signifier is associated with one and only one signified, we call this a symbolic system. Traffic lights and the "language" of flowers are examples of symbolic systems (roses = 'love', tulips = 'friendship', etc.). A system is semi-symbolic if an opposition between signifiers corresponds (is homologous) to an opposition between signifieds. Gestures are often semi-symbolic in nature, as in the opposition vertical movement/horizontal movement, which is homologous to the opposition 'yes'/'no'. Traffic signals meet this definition partially: while red and green are in opposition as complementary colours, yellow does not have a real opposite in this system. Be that as it may, in other contexts each of these three colours can be part of other culturally defined oppositions (either within one culture or between cultures). For example, red and black are in opposition in several cultures, particularly in Africa. (3) Lastly, other systems may be classified as semiotic. Language is such a system.