What is ESD protection, Bi-directional communication, ESD protection circuit

PGB1 Series 250 V 0.04 pF Bi-Directional 0402 SMT PulseGuard® ESD Suppressor Website URL: https://www.futureelectronics.com/p/electromechanical–circuit-protection–esd-protection/pgb1010402kr-littelfuse-6417943 Country List: Bangladesh