What does YUS stand for? 

Yus

Little yus and big yus, or jus, are letters of the Cyrillic script, representing two Common Slavonic nasal vowels in the early Cyrillic and Glagolitic alphabets. Each can occur in iotified form, formed as ligatures with the letter Decimal I. Other yus letters are blended yus, closed little yus and iotified closed little yus. Phonetically, Little yus represents a nasalized front vowel, possibly, while big yus represents a nasalized back vowel, such as IPA. This is also suggested by the appearance of each as a 'stacked' digraph of 'Am' and 'om' respectively. The names of the letters do not imply capitalization: both little and big yus exist in majuscule and minuscule variants. All modern Slavic languages that use the Cyrillic alphabet have lost the nasal vowels, making yus unnecessary. Big Yus was a part of the Bulgarian alphabet until 1945. However, by that time the back nasal was pronounced the same way as ъ. As a result, there were inconsistencies in its usage since people had to rely on memorized orthographic conventions to put it in its etymologically correct place. There are some Macedonian dialects around Thessaloniki and Kastoria in Northern Greece that still preserve a nasal pronunciation, 'Where are you going, dear child?'.

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