What is krechtz?
קרעכץYiddishalso spelled krekhtsPronunciation: Jewish English Lexicon (CC BY-SA 4.0)
Yiddish for 'sob' or 'groan' — the little cracking catch a klezmer (כּלי־זמר) clarinet or violin puts on the tail of a note, imitating a voice breaking. It's much of why klezmer seems to weep and laugh at once.
The krechtz (plural krekhtsn) is the most famous of the klezmer ornaments: a short, throaty break added to the end of a sustained note — on the violin a ghostly touched harmonic, on the clarinet a swallowed hiccup up to a higher partial — that makes the instrument 'sob' the way a cantor's voice cracks on a word of prayer. Together with slides, bent pitches, and trills, it's part of a whole vocabulary of vocal imitation: klezmer treats the instrument as a voice davening (דאַוונען), which is why the same tune played straight from the page stops sounding like klezmer at all.