、「

For example, the opposite of 'joy' is 'sorrow.'

Literal

For-example, 'joy' [of-の] opposite [topic-は] 'sadness' [copula-です].

反対語 ('opposite word, antonym') is a technical linguistic term. The 「」 quotation marks highlight the words being discussed — standard convention when citing words as words. A vocabulary-teaching sentence.