An ESD (short for electrostatic discharge) is a powerful device that deploys an electrostatic field in a wide area for a short period of time. It is related to the electromagnetic pulse based weapons of the late 20th and early 21st century.
Unlike traditional EMPs, this weapon does not damage electronics or destroy advanced technology if they are appropriately protected with Anti-ESD systems or when being grounded. It just disables technology within a certain radius for a specific amount of time, after which most technology restarts/reboots.
Most civilian vehicles, damaged military vehicles or Nanotech are not protected against the effects of an ESD. So far only one version of the ESD has been seen in-series, in the form of an air-dropped weapon primarily used by the Vanguard's Interceptors.
The weapon is functionally a gravity bomb, having no propulsion system and relying only on the kinetic energy, provided by carrying aircraft. It presumably has some guidance ability (due to presence of some kind of concavity on the nose and forward fins). In action, the weapon is usually either dropped, or toss bombed by the aircraft, requiring certain altitude to be effective.
Interceptors are capable of carrying and launching them. A certain amount of authority is required to use them, as Simone Rasmussen requests Colonel Raquel Marin's permission to use it against Nanotech and a Behemoth.