The prefix "counter-" is used to indicate opposition or contrast. It often appears in words to signify actions or concepts that go against something else. For example, in the word counteract, it refers to taking action to reduce or negate the effects of another action. In addition to its use in verbs, "counter-" can also describe physical objects or locations. A countertop is a flat surface in kitchens or stores where activities like food preparation or sales occur. Overall, "counter-" serves as a versatile prefix that highlights opposition or interaction with other elements.