In its most general sense, and especially as defined by structuralist studies of human institutions and behaviour, the term applies to the main abstract characteristic of a semiotic system. A language, for example, is a structure, in the sense that it is a network of interrelated units, the meaning of the parts being specifiable only with reference to the whole. More specifically, the term is used to refer to an isolatable section of this total network, as in the discussion of the structure of a particular grammatical area.

However, this application of the term to paradigmatic relationships is not as widespread as the syntagmatic conception of ‘structure’. Here a particular sequential pattern of linguistic elements is referred to as ‘a structure’, definable with reference to one of the various ‘structural levels’ recognized in a theory, e.g. ‘phonological structure’, ‘syntactic structure’, ‘morphological structure’, ‘semantic structure’. The set of items which contrast at a particular ‘place’ in a structure is then referred to as a system. This is the way in which the term is used in Hallidayan linguistics, for example, where it has a special status, as the name of one of the four major categories recognized by the theory: the category of ‘structure’ accounts for the ways in which an occurrence of one syntactic unit can be made up out of occurrences of the unit below it. In this sense, the morpheme has no structure, being the minimal unit in grammar.