The letter Ъ ъ of the Cyrillic script is known as er goläm in the Bulgarian alphabet, as the hard sign in the modern Russian and Rusyn alphabets, as the debelo jer in pre-reform Serbian orthography, and as ayirish belgisi in the Uzbek Cyrillic alphabet. The letter is called back yer or back jer and yor or jor in the pre-reform Russian orthography, in Old East Slavic, and in Old Church Slavonic.

The Cyrillic script, Slavonic script or simply Slavic script is a writing system used for various languages across Eurasia. It is the designated national script in various Slavic, Turkic, Mongolic, Uralic, Caucasian and Iranic-speaking countries in Southeastern Europe, Eastern Europe, the Caucasus, Central Asia, North Asia, and East Asia, and used by many other minority languages.