The phrase 'mons altus est' translates to 'the mountain is high' in English. This term illustrates the use of predicate nominatives and adjectives in Latin, where 'mons' (mountain) serves as the subject, 'altus' (high) functions as an adjective describing the subject, and 'est' (is) acts as the linking verb. This structure demonstrates how Latin connects subjects with their descriptions, emphasizing the relationship between a noun and its qualities.