KOI7 is a 7-bit character encoding, designed to cover Russian, which uses the Cyrillic alphabet. It covers only capital latin and cyryllic letters due to its 7-bitness.
In Russian, KOI7 stands for Kod Obmena Informatsiey, 7 bit (Код Обмена Информацией, 7 бит) which means "Code for Information Exchange, 7 bit".
See also