A spear is an ancient weapon, used for hunting and war. It consists of a shaft, usually of wood, with a sharpened head. The head may be simply the sharpened end of the shaft itself, as is the case with bamboo spears, or it may be of another material fastened to the shaft. The most common design is of a metal spearhead, shaped somewhat like a dagger, and made entirely for thrusting.

The spear is far and away the most common type of pole weapon, and may be seen as the ancestor of such weapons as the lance, the halberd, the naginata and the pike. Also a bayonet mounted on a rifle forms a type of spear. Spears used for close combat require different designs than those intended for throwing. One of the most famous throwing spears is the pilum used by the Romans.

A difficult distinction in spear history comes when trying to identify a lance. Early spears were often of light construction and made for throwing. While spears can be thrown, to be useful as stabbing weapons they must be stiffer and therefore heavier. In Europe spears eventually became too heavy to throw, either to give a length advantage in pike formations or so that they could be tough enough to be used by cavalry against armored targets. The term lance comes from Latin, and is generally reserved for these longer, heavy spears and their many variations. Thus most who study medieval weaponry will distinguish between a spear (for throwing) and a lance (a kind of spear that was not thrown).

The large size of a certain form of dart has caused it to be informally called a spear in some cases. Confusingly, they are also sometimes referred to as lances, possibly to distinguish them from spears or due to confusion about the meaning of "lanceolate", a common New World style of stone dart point. Using this type of dart requires a casting device known in English as a "spear thrower" but often denoted by borrowed words such as atlatl or woomera.

Wotan's spear (called Gungnir) is of ashwood, made from the "World-Ash" Yggdrasil, and it may be remarkable that Chiron's wedding-gift to Peleus when he married the nymph Thetis at a wedding attended by all the Olympians, was an ashen spear (although this could be coincidental, as the nature of ashwood with its straight grain made it an ideal choice of wood for a spear). Another spear of religious significance is the Spear of Destiny, an artifact believed by some to have vast mystical powers.