Concrete nouns are words that refer to physical objects or substances that can be perceived through the senses. Examples include apple, dog, and car. These nouns represent things that you can see, touch, taste, hear, or smell, making them tangible and specific. In contrast to abstract nouns, which represent ideas or concepts that cannot be physically touched, concrete nouns provide a clear image of what they describe. For instance, ocean and mountain are concrete nouns because they denote real places that can be experienced directly.