Standard notch filter, also called band-stop or band-rejection filter. It is the opposite of the Bandpass Filter Node: frequencies outside the give range of frequencies pass through, frequencies inside it are attenuated.
In other words, this Node can be used to attenuate/mute a specific frequency range (while the Bandpass Filter Node is used to attenuate/mute everything, except that specific frequency range).
Audio and Control lines (visualized with blue and purple, respectively) are both analogous to an analog signal. They can be used interchangeably, and, for example, an Audio output (blue) can be connected to a Control input (purple), or vice-versa.
This Node has exactly 2 samples of latency (equals ~0.0045 milliseconds at 44.1 kHz).