Antimatter was described in many different ways.
After Jenna experimented with Liberator's controls and sent the ship hurtling forward at high speed, Kerr Avon mentioned "negative hyperspace", to which Blake responded: "Do you mean we crossed the antimatter interface?".
Roj Blake described the thousands of objects discovered by Avon out beyond Star One as "the biggest antimatter minefield ever put together". The mine-field also acted as an early warning system. (B: Star One)