The Eurondan defense field is a piece of defensive technology used by the Eurondans.
The defense field is very similar to a shield used by other races. The field is powered by Heavy water and could withstand a squadron of Breeder fighters, as long as the field is powered. The field is operated by a large cylidrical tunnel, running with several slow moving fans. If the tunnel is destroyed, the field would no longer work, and the underground bunker would become vulnerable to attack.
When SG-1 learned of the defense field, they discovered that heavy water is what it needs to power it. Since the Breeders took control of much of Euronda's water supply, SG-1 managed to have sent some to power it. However, after learning that the Eurondans planned the extermination of the Breeders, O'Neill used the Remote Flyer to crash the aerofighter into the field generator. The bunker became vulnerable, and the was most likely destroyed. (SG1: "The Other Side")