Superlative adjectives are used to describe the highest degree of a quality among three or more items. They often end in "-est" or are preceded by the word "most." For example, in the phrase "the tallest building," the adjective "tallest" indicates that this building is taller than all others in comparison. These adjectives help to highlight differences and make comparisons clearer. Common examples include fastest, smartest, and largest. When using superlative adjectives, it’s important to ensure that the comparison involves at least three subjects to maintain grammatical accuracy.