The scheduled time for the start of some event, especially a military operation; H-hour.

Of any system where all gains are offset by exactly equal losses.

(physics, quantum mechanics) The lowest possible energy of a given quantum mechanical system.

The strict policy of enforcing all the laws of a state, or the rules of an institution, and allowing no toleration or compromise even for first-time offenders or petty violations.

(game theory) A game (or a similar political or economic system) in which the gains of some players must equal the losses of others.

(chiefly Britain) subject to no value-added tax when sold (but the supplier can still recover VAT attributable to it)

simple past tense and past participle of zero-rate

Originally, the point on the land or water surface below which a nuclear bomb detonates in the air; now also the point on such a surface at or above the detonation.

(of a temperature) below 0°C; freezing cold

(American football) an infraction in which a football player, on defense, gets into or crosses the neutral zone during the snap, causing an offensive player to false start. The penalty is against the defense, not the offense. It is a 5 yard penalty.