A torpedo is defined as a weapon that is typically guided and powered through water, designed to be launched from submarines, surface ships, or aircraft to target enemy vessels. This type of weapon is specifically engineered to travel beneath the water's surface to reach its target, often employing propulsion mechanisms that allow it to maneuver effectively and hit moving ships or submarines. The guidance systems can vary, ranging from acoustic homing to wire guidance, enabling improved accuracy and effectiveness.
The other options present alternative types of munitions. The second option describes an unguided air-to-ground explosive device, which does not fit the specific characteristics of a torpedo. The third option refers to a floating explosive device, which is unrelated to the submerged operation of torpedoes. Lastly, the fourth option discusses a weapon designed for use from aircraft onto land, which is characteristic of bombs or missiles, not torpedoes. Thus, the definition of a torpedo as a guided weapon that moves through water is accurate and encompasses its primary function and operational use in naval warfare.