In phonology, the ts-ch merger is the merger of the voiceless alveolar affricate and the voiceless postalveolar affricate.
In Russian language it is the merger of the consonants rendered by letters Che and Tse. If the shift is towards Tse, it is called tsokanye (цоканье); the shift towards Che is called chokanye (чоканье).
In Polish language the cz->c merger is part of a more general dialectal feature called Mazurzenie, after the dialect of Mazovia. It also occurs in a few areas of the Chakavian dialect of Croatian, known as tsakavism.
The sabesdiker losn feature of Northeastern Yiddish includes the ch->ts merger.