The superlative degree is a grammatical form used to express the highest degree of a quality among three or more items. It often involves adding the suffix "-est" to an adjective, such as in the word tallest, or using "most" before adjectives that do not take the suffix, like most beautiful. Superlatives help to compare one item against all others in a group. For example, in the sentence "Mount Everest is the highest mountain," "highest" indicates that Mount Everest surpasses all other mountains in height.