A polearm is a category of weapons that encompasses a variety of long-handled melee weapons designed for close combat. The term "spear" is one specific type of polearm. While there is some overlap in their definitions, there are distinctions between the two:

1. Design: Spears typically have a long shaft with a pointed blade or head at one end, designed primarily for thrusting attacks. The head of a spear can have various shapes, including leaf-shaped, triangular, or diamond-shaped. In contrast, polearms encompass a broader range of weapons with different designs, such as halberds, glaives, billhooks, and poleaxes. These weapons often combine a spear-like thrusting tip with additional features like axes, hooks, or blades.
2. Versatility: Spears are generally straightforward and specialized for thrusting, providing reach and penetration against opponents. Polearms, on the other hand, often have multiple functionalities. They may combine thrusting, cutting, and hooking capabilities, making them more versatile in combat. Polearms are designed to exploit the advantages of a long shaft while offering a variety of offensive and defensive techniques.
3. Historical Usage: Spears have been used as weapons throughout history and across cultures, dating back to ancient times. They were commonly employed by foot soldiers and were renowned for their simplicity, effectiveness, and affordability. Polearms, including spears, gained popularity during the medieval period and continued to be widely used until the advent of firearms. They were often employed by both infantry and cavalry units.

Overall, the key distinction between a spear and a polearm lies in the broader category of polearms encompassing a variety of weapons, while a spear refers specifically to a long-handled weapon with a pointed tip primarily designed for thrusting attacks.