What is "iotation"

n. 1 (context linguistics English) A specific occurrence of palatalization that occurred in the Proto-Slavic language, in which a consonant combined with the palatal approximant (IPAchar: /j/) to form a palatalized consonant. 2 (context linguistics English) Any similar process occurring in a later Slavic language or elsewhere.

In Slavic languages, iotation is a form of palatalization that occurs when a consonant comes into contact with a palatal approximant /j/ from the succeeding morpheme. The /j/ is represented by iota (ι) in the Cyrillic alphabet and the Greek alphabet on which it is based. For example, ni in English onion has the sound of iotated n. Iotation is a distinct phenomenon from Slavic first palatalization in which only the front vowels are involved, but the final result is similar.