(1) A term used in phonology to refer to the distinctive pitch level of a syllable. In the study of intonation, a sequence of tones constitutes a contour or tone unit. In Hallidayan analysis, the division of an utterance into tone groups is called tonality. The most prominent tone in a tone unit may be referred to as a nuclear tone. In many languages, the tone carried by a word is an essential feature of the meaning of that word (lexical tone), e.g. in Beijing Mandarin Chinese the word ma when pronounced in a level tone means ‘mother’, and in a falling-rising tone means ‘horse’ - two out of four possible tone contrasts in that language. Such languages, where word meanings or grammatical categories are dependent on pitch level, are known as tone languages. The unit which carries the tone (e.g. syllable, mora) is called the tone-bearing unit. Many languages of South-East Asia and Africa are tone languages, illustrating several types of tonal organization. In such languages, sequences of adjacent tones may influence each other phonetically or phonologically, e.g. a word which in isolation would have a low tone may be given higher tone if a high-tone word follows: such a phenomenon is sometimes called tone (or tonal ) sandhi. The organization of tonal structure within a non-linear phonological model (the nature of tonal features and the location of tonal linkage) is sometimes called tonal geometry.

The study of the phonetics properties of tone, in its most general sense, is sometimes referred to as tonetics. In the emic tradition of study, contrastive tones are classified as tonemes, and the study of such tones is known as tonemics. Features of tone, such as ‘high’, ‘low’ and ‘mid’, are proposed by distinctive feature theories of phonology. Tones which vary in pitch range are often called ‘contour’, ‘kinetic’ or ‘dynamic’ tones; those who do not vary in range are ‘static’ or ‘level’ tones.

(2) In acoustic phonetics, a sound with sufficient regularity of vibration to provide a sensation of pitch. Sounds which lack this regularity are characterized as noise. A pure tone is produced by a waveform whose pattern of vibration repeats itself at a constant rate; such tones are typically produced by electronic sources or tuning forks. When two or more tones of different frequencies combine, the result is a complex tone. Most sounds, including those of speech, involve complex tones, with different periodic patterns.