ESD (Electrostatic Discharge), is the rapid disengaging of electrical energy arosing from electro-static source; equalization of potential difference.
In case of the presence of such electrical energy and its discharge on electrical sensitive devices, spares can loose their optimal features or their values may change. The sensitivity of a given device depends on the components and the structure. The smaller and faster the device, the more sensitive it is.
The rate of discharge depends on several factor such as humidity or materials in friction... Examples in life: getting out from our car on the shell, after walking on PVC, laminated floor, carpets by touching metal or electrical equipments (e.g. computer) or by a simple handshake.
Walking on carpet:
by 10-20 % humidity content 35000 V
by 65-90 % humidity content: 1500 V
The best protection is preventing electro-static discharge combined with deduction of charges being present, if any.