Electrostatic discharge (ESD)
also: ESD · static discharge · IEC 61000-4-2
The sudden discharge of static electricity from a person or object into a device, which can reset, damage or destroy electronics that aren't designed for it.
A person can easily build up several thousand volts of static charge; touching a product dumps it into whatever path it finds. Exposed connectors, buttons, enclosure seams and touchscreens are the entry points. The common system-level test standard, IEC 61000-4-2, defines contact-discharge test levels of 2, 4, 6 and 8 kV and air-discharge levels up to 15 kV; the product standard you test to says which levels apply.
Protection combines enclosure design (keeping conductive parts away from seams and openings), PCB design (transient-voltage-suppression diodes close to connectors, ground paths that steer the current away from sensitive chips) and firmware that recovers cleanly from a glitch.
ESD also matters in the factory: poor handling can damage parts before they ship, creating latent failures that appear later in the field.
Founder takeaway
List every point a user can touch, protect each on the board and in the enclosure, and test to the levels your product standard requires.
engineer review pending