What does CHECKED TONE stand for? 

Checked tone

A checked tone, commonly known by the Chinese calque entering tone, is one of the four syllable types in the phonology of Middle Chinese. Although usually translated as "tone", a checked tone is not a tone in the phonetic sense but rather a syllable that ends in a stop consonant or a glottal stop. Separating the checked tone allows -p, -t, and -k to be treated as allophones of -m, -n, and -ng, respectively, since they are in complementary distribution. Stops appear only in the checked tone, and nasals appear only in the other tones. Because of the origin of tone in Chinese, the number of tones found in such syllables is smaller than the number of tones in other syllables. In Chinese phonetics, they have traditionally been counted separately. For instance, in Cantonese, there are six tones in syllables that do not end in stops but only three in syllables that do so. That is why although Cantonese has only six tones, in the sense of six contrasting variations in pitch, it is often said to have nine tones. Final voiceless stops and therefore the checked "tones" have disappeared from most Mandarin dialects, spoken in northern and southwestern China, but have been preserved in the southeastern branches of Chinese, such as Yue, Min, and Hakka. Tones are an indispensable part of Chinese literature, as characters in poetry and prose were chosen according to tones and rhymes for their euphony. This use of language helps the reconstruction of the pronunciation of Old Chinese and Middle Chinese since the Chinese writing system is logographic, rather than phonetic.

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