A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, relationship, or mathematical formula. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise different concepts and experiences. All communication is achieved through the use of symbols: for example, a red octagon is a common symbol for "STOP"; on maps, blue lines often represent rivers; and a red rose often symbolizes love and compassion. Numerals are symbols for numbers; letters of an alphabet may be symbols for certain phonemes; and personal names are symbols representing individuals. The academic study of symbols is called semiotics.

In the arts, symbolism is the use of a concrete element to represent a more abstract idea. In cartography, an organized collection of symbols forms a legend for a map.

The word symbol derives from the late Middle French masculine noun symbole, which appeared around 1380 in a theological sense signifying a formula used in the Roman Catholic Church as a sort of synonym for 'the credo'; by extension in the early Renaissance it came to mean 'a maxim' or 'the external sign of a sacrament'; these meanings were lost in secular contexts. It was during the Renaissance in the mid-16th century that the word took on the meaning that is dominant today, that of 'a natural fact or object evoking by its form or its nature an association of ideas with something abstract or absent'; this appears, for example, in François Rabelais, Le Quart Livre, in 1552. This French word derives from Latin, where both the masculine noun symbolus and the neuter noun symbolum refer to "a mark or sign as a means of recognition." The Latin word derives from Ancient Greek: σύμβολον symbolon, from a verb meaning 'put together', 'compare', alluding to the Classical practice of breaking a piece of ceramic in two and giving one half to the person who would receive a future message, and one half to the person who would send it: when the two fit perfectly together, the receiver could be sure that the messenger bearing it did indeed also carry a genuine message from the intended person. A literary or artistic symbol as an "outward sign" of something else is a metaphorical extension of this notion of a message from a sender to a recipient. In English, the meaning "something which stands for something else" was first recorded in 1590, in Edmund Spenser's Faerie Queene.

Symbols are a means of complex communication that often can have multiple levels of meaning. Symbols are the basis of all human understanding and serve as vehicles of conception for all human knowledge. Symbols facilitate understanding of the world in which we live, thus serving as the grounds upon which we make judgments. In this way, people use symbols not only to make sense of the world around them but also to identify and cooperate in society through constitutive rhetoric.

Human cultures use symbols to express specific ideologies and social structures and to represent aspects of their specific culture. Thus, symbols carry meanings that depend upon one's cultural background. As a result, the meaning of a symbol is not inherent in the symbol itself but is culturally learned.

Heinrich Zimmer gives a concise overview of the nature, and perennial relevance, of symbols.

Concepts and words are symbols, just as visions, rituals, and images are; so too are the manners and customs of daily life. Through all of these, a transcendent reality is mirrored. There are so many metaphors reflecting and implying something which, though thus variously expressed, is ineffable, though thus rendered multiform, remains inscrutable. Symbols hold the mind to truth but are not themselves the truth, hence it is delusory to borrow them. Each civilisation, every age, must bring forth its own."

In the book Signs and Symbols, it is stated that