The word "by" is a preposition that indicates a relationship between an action and the agent or means by which it is performed. It often signifies proximity, direction, or the manner in which something is done. For instance, it can describe the person who performs an action, the method used, or the approach taken to achieve a result.
The word "by" originates from the Old English "bi," which meant "near, close to, or in the presence of." Its usage has evolved over centuries to encompass various meanings in contemporary English.