The term "cog" has a few different meanings. It can refer to a tooth on the rim of a wheel or gear, a gearwheel, especially a small one, or a person who plays a minor part in a large organization or activity
. In the context of a person, it is often used to describe someone who performs an important but routine function within a larger system. For example, someone might say, "I'm just a cog in the system" to express feeling disheartened about their role
