ESD is electrostatic discharge: https://en.wikipedia.org/wiki/Electrostatic_discharge
The human body is a walking Van de Graff generator, with a license to kill any components, particularly (but not limited to) insulated gate CMOS inputs. Gobs of die area is devoted to diodes and the like in an attempt to make CMOS safe to handle with human hands and the like. Even things like capacitors aren't immune to ESD, and partial degradation is often worse than outright failure. Ignore it at your peril, you have been warned. Those who design Theremins tend to not think about ESD, but tying high Q sensitive circuitry to bare metal rods that get man handled is just asking for it (and then some because an ESD discharge could cause many "events" as the tank rings down). The very least you should do is insulate your antennas.
All modern components are packaged in conductive bags and trays for good reason.
