The term 'superlative ending' refers to the suffixes that are added to adjectives to denote the highest degree of comparison. The two most common superlative endings are 'iest' and 'est'. The suffix '-iest' is used for words with more than two syllables, while the suffix '-est' is used for words with two syllables or less. For example, the word 'BEAUTIFUL' would become 'most BEAUTIFUL' with the addition of the '-iest' suffix. Similarly, the word 'FAST' would become 'fastest' with the addition of the '-est' suffix.