A Proximity Warhead is any projectile weapon (missile, cannon shell, etc.) designed to explode near a target instead of hitting it directly. More specifically, in space combat terms, it is a missile or torpedo with a small fusion bomb for a warhead, designed to explode within a few miles of its target and damage it with shrapnel (there being no atmosphere in space to produce a shockwave). The fusion warhead is small, because a big one would just vaporize the warhead casing and turn it into plasma…which can be easily deflected with the magnetic fields used to deflect micrometeorites. Instead, the warhead casing is made of a blast-resistant material such as tungsten, and often further surrounded by small pre-fragmented pieces of tungsten or other tough, hard-to-vaporize metal, designed to become shrapnel thrown outward at extreme velocities by the blast. If a proximity warhead detonates close enough to its target, the hard radiation can cause additional damage, but just to survive in outer space most ships are heavily armored and shielded against cosmic rays anyways.