Róuyīn 揉音

A category of deep vibratos that are pressed so strongly the string reaches the next highest note. They are played by pressing and releasing the strings to the left of the movable bridges, typically by the index, middle, and ring fingers held together. Two other possible terms for this are da zhanyin 大颤音 and rou xian yin. Ferguson’s Sources E and F say it is a slow rhythm, only pressing the string 2 or 3 times in the space of a quarter note.

Also note: some sources say rouyin is a light vibrato whereas Ferguson cites a strong vibrato played with more strength or power and that goes to a higher pitch than any of the other yín/yīn vibratos.