(or " connotation") refers to the meaning or characteristics encompassed by a given word, often expressed by a definition.

Intension is often discussed with regard to extension. Intension refers to the set of all possible things a word could describe. By contrast, extension (or denotation) refers to the set of all actual things the word describes. For example, the intension of 'car' is all possible cars (including mile-high cars made of chocolate). But the extension of 'car' is all actual cars (past, present and future), which will amount to millions or billions of cars, but probably doesn't include any mile-high cars made of chocolate.

Intension is an essential part of meaning. The meaning of a word is the bond between the idea or thing the word refers to and the word itself. Useful here is Swiss linguist Ferdinand de Saussure's concept of the signified -- the concept or idea that a sign evokes. We can contrast the signified with the signifier -- the "sound image" or string of letters on a page that one recognises as a sign -- and with the referent, the actual thing or set of things a sign refers to. Intension is analogous to the signified; extension, to the referent. The intension thus links the signifier to the sign's extension. Without intension of some sort, words can have no meaning.

Intension and intentionality (the state of having intension) should not be confused with intention and intentionality, which are pronounced the same and occasionally arise in the same philosophical context. Where this happens, the letter 's' or 't' is sometimes italicised to emphasise the distinction.