are a series of alternate fingerings used for the throat tone notes on a clarinet. They improve the tone and tuning and make the transition between registers more seamless (and easier as well).
This is a very variable register of the clarinet in terms of pitch and tone quality.Since they are short tube notes (made with not many holes closed) any change in your embouchure, tongue position or air pressure will be much more noticeable than it would be with a long note (meaning a note fingered with all the fingers down.) Resonant fingerings have the additional benefit of making these notes more resistant and therefore more stable. Most of the resonant fingerings also lower the pitch of the throat tones, which are often sharp .In the throat tone range the clarinet can easily go from being very flat to very sharp on any note depending on how loudly the note is played.
Read more: Resonant fingerings