The phrase 'pueri boni sunt' translates to 'the boys are good' in English and serves as an example of a complete sentence in Latin that illustrates the use of predicate nominatives and adjectives. In this phrase, 'pueri' (boys) is the subject in the nominative case, 'boni' is the predicate adjective describing the subject, and 'sunt' is the verb meaning 'are.' This construction highlights how nouns can be linked to adjectives to convey specific characteristics.