The term "certain" refers to something that is definite, specific, or known without doubt. It is often used to indicate a level of assurance or confidence about a particular fact or situation. For example, when someone says they are "certain" about a decision, it means they have a strong belief in its correctness. In everyday language, "certain" can also describe a specific group or category. For instance, one might refer to "certain people" or "certain conditions," highlighting that not everyone or everything falls into that category. This usage helps to clarify and narrow down discussions or statements.