What are TVS diodes (ESD protection diodes)?

They are a type of Zener diode. They are mainly used as a measure against electrostatic discharge (ESD). They are generally used for protecting ICs from ESD that comes from USB line. They have low capacitance between electrodes so as not to affect signal, and low resistance (R_dyn) to improve the protection function. Products supporting positive and negative direction ESD have recently become mainstream.