Use the fifth finger to pluck in a closing motion, toward the palm. If using own nail, the nail (if long enough) and pad contact the string.

“Yin” is a term offered by Kwok 1987. Cheng 1991 offers “rou zhi bo xian” and Ferguson 1979 Xiǎozhǐ nèi tán 小指内彈, "little finger plucks inward".

The character is unconfirmed. If you know, please share!