A tone contour is a tone in a tonal language which shifts from one pitch to another over the course of the syllable or word. Tone contours are especially common in East and Southeast Asia, but occur elsewhere, such as the Kru languages of Liberia and the Ju languages of Namibia.
Chart(which is said to be invented by a Chinese linguist Yuen Ren Chao) illustrating the contours four tones in Standard Chinese
When the pitch descends, the contour is called a falling tone; when it ascends, a rising tone; when it descends and then returns, a dipping or falling-rising tone; and when it ascends and then returns, it is called a peaking or rising-falling tone. A tone in a contour-tone language which remains at approximately an even pitch is called a level tone. Tones which are too short to exhibit much of a contour, typically because of a final plosive consonant, may be called checked, abrupt, clipped, or stopped tones.
There are three phonetic conventions for transcribing tone contours.
Diacritics such as falling 〈â〉, rising 〈ǎ〉, dipping 〈a᷉〉, peaking 〈a᷈〉, high falling 〈a᷇〉, low falling 〈a᷆〉, high rising 〈a᷄〉 and low rising 〈a᷅〉. Or the simpler register tones, where diacritics such as high 〈á〉, mid 〈ā〉, and low 〈à〉 are usually sufficient for transcription. (These are also used for high, mid, and low level contour tones.)
Tone letters such as mid level 〈˧〉, high falling 〈˥˩〉, low falling 〈˨˩〉, mid rising 〈˧˥〉, low rising 〈˩˧〉, dipping 〈˨˩˦〉, and peaking 〈˧˦˩〉.
Numerical substitutions for tone letters. The seven tones above would be written 〈33〉, 〈51〉, 〈21〉, 〈35〉, 〈13〉, 〈214〉, 〈341〉, for an Asian language, or 〈33〉, 〈15〉, 〈45〉, 〈31〉, 〈53〉, 〈452〉, 〈325〉, for an African or American language. (The doubling of the numeral in 〈33〉 in the level tone is used to disambiguate from a "tone 3", which in general is not at pitch level 3.)