Abbreviation for Improvised Explosive Device. A home-made bomb, although it doesn't have to be made at home as it can quite easily be made at the workplace or in the garden shed. It is the Ammunition Technician that form the EOD teams of the RLC who specialize in rendering IEDs safe.
Currently the weapon of choice in Iraq for blowing up Iraqi Civies and passing military patrols. Likely to become the favoured weapon in Afghanistan since unlike the Ruskies in the 80's, our guys can actually hit what they are shooting at and the Taliban are likely to get fed up being shot to shit.
See also EOD
Much like Walkers crisps, or lip balm, IEDs come in many flavours, ranging from little snap, crackle and pop to big boom boom. The intended target largely determines what size bang is required for maximum effect, and how the bang needs to come about. These fall vaguely into the following:
Victim Operated IEDs; sometimes known as explosive Booby Traps, where you, the intended target, initiate a device through your own actions. These days it usually requires stepping on something, but horrible people throughout history have thought long and hard about how to kill and maim people, and so there are some exceptionally elaborate ways of causing someone to blow themselves up. See IRA.
Timed IEDs; ah, the classic countdown timer. Often a red pack of dynamite with a ticking clock on it. Easy to spot if you look a bit.
Command IEDs; where Terry Taliban is required to initiate the device when he so chooses in order to send people to the afterlife. This covers everything from command wires, to radio control, and all that good stuff.