Plain English Meaning
It is the flashing light unit inside a modern airport beacon that sends out a quick, bright burst of light in every direction at once, instead of spinning a steady bulb around to create the flash effect.
Full Definition
A high-intensity flashing light source used in modern airport rotating beacons that produces brief, powerful flashes of light visible in all horizontal directions by rapidly discharging stored electrical energy from a capacitor through a gas-filled tube, rather than rotating a continuous lamp.
Context Anchor
Seen in airport beacon descriptions, especially when explaining how some airport beacons flash without using a rotating light.
Derivation
Omnidirectional comes from the Latin omni, meaning all, plus directional, so light goes out in all directions. Capacitor-discharge describes how the device works: a capacitor stores up electrical energy and then releases it all at once to produce a bright flash. Together the name tells you what it does and how it does it.