A DC offset remover.
This is a highpass filter with a cutoff of 159 mHz, which is far less than the generally accepted lower limit of human hearing (20Hz). Thus, no audible content is lost, and even signals as low as 1Hz pass though with negligible attenuation.
A 50V ceramic capacitor is used.
The switch indicates the internal switch of the audio input jack. It is grounded when no plug is inserted.
