Also alveo-palatal. In phonetics, this refers to sibilants made in the postalveolar region (between the alveolar ridge and the palate), with an additional "softening".

The precise description of this softening is, I believe, disputed. It has been described as palatalization, but that is insufficient in terms of tongue position: I find I lower the tip of my tongue, but I am not only not a native speaker of Polish or Chinese, I have not been taught by one either, so I can't be precise about it.

In Polish they are the sounds written ś ź ć dź with acute accents over them, or plain s z c dz before the letter i. These sounds contrast with both the ordinary (unaccented) s z c dz, and with the postalveolar (formerly called palato-alveolar) sounds sz rz cz drz, which are the equivalent of English sh ch j.

In Chinese they are written x q j in Pinyin transcription, as in Qinghai or Beijing. The fact that these were formerly written Tsinghai, Peking in the Wade-Giles transcription shows that the alveolo-palatal sounds of the modern Beijing dialect are recent developments before the vowels i and ΓΌ. They only occur before those two vowels (the u is written without its umlaut for simplicity). Chinese doesn't have the sh ch j sounds of English or Polish: but its alveolo-palatal sounds contrast with the retroflex consonants written as sh r ch zh, as well as the ordinary alveolar sibilants written s c z.

In Japanese alveolo-palatals occur in the syllables ti si zi, tya sya zya etc., which are often romanized as chi shi ji, cha sha ja.