A Sonnet has a final couplet when it has - WAEC Literature 2018 Question

The English sonnet (also called the Shakespearean sonnet after its foremost practitioner) comprises three quatrains and a final couplet, rhyming ababcdcdefefgg. An important variant of this is the Spenserian sonnet (introduced by the Elizabethan poet Edmund Spenser), which links the three quatrains by rhyme, in the sequence ababbabccdcdee. In either form, the 'turn' comes with the final couplet, which may sometimes achieve the neatness of an epigram.