A warhead is the part of a military weapon, of a weapon type that physically moves to a target, the warhead causing the desired destructive effect. Artillery externally applies energy to the device containing the warhead, or the warhead may be part of a self-propelled weapon (e.g., unguided rocket, torpedo, guided missile. An artillery warhead, and its mechanical case, is often called a projectile. A destructive device that is not externally or self-propelled is called a bomb.
Warheads also have a means of deciding when to trigger the effect, such as a fuze or a communications link over which a triggering signal is received (i.e., command detonation. Air-delivered warheads, for example, may have fuzes that act immediately on contact with the target, or delay slightly so the warhead casing can penetrate into the target. A warhead may have a proximity fuze so that it detonate at some altitude above the ground.
The effect is most commonly explosive blast, but could be intense heat (i.e., incendiary, blast and small pieces of fast-moving metal (e.g., blast-fragmentation, or a nuclear exlosion. Warheads may release chemical warfare or biological warfare agents.
A ballistic missile may have multiple warheads of different types, mounted im specialized reentry vehicles. Ballistic missiles, of course, also can have but a single warhead.
Some precision-guided munitions, while physically large guided missiles, do not contain any destructive material in their warhead, but still have an inert warhead filled with an inert material such as concrete. Such a warhead still has a destructive effect, as it is only used with weapons that move extremely fast, acquiring large amounts of kinetic energy. The kinetic energy of a concrete-filled ballistic missile warhead, or of the collision of an anti-ballistic missile with the incoming ballistic missile warhead(s). The kinetic energy of a ballistic missile is so great that adding a chemical explosive would not add significantly to the energy transferred to the target.
Warheads on weapons traveling much more slowly may have inert fillers, or perhaps a chemical that generates smoke. Such warheads are used for training and practice.