Google is your friend here:
Half harmonics occur when the string is depressed by the left-hand finger somewhere between normal, stopped pressure and harmonic pressure. The sound is a mixture of the stopped string pitch, the harmonic pitch, and a resistant, slightly noisy quality. The stopped-string pitch is often also present in multiphonics.
https://cellomap.com/multiphonics-other-multiple-sounds/
For winds multiphonics see for example this thread:
and this link:
and here: