What type of poem is defined as having 3 quatrains and an ending couplet with a rhyme scheme of abab, cdcd, efef, gg?

The type of poem defined by having three quatrains followed by a couplet, and adhering to the specific rhyme scheme of abab, cdcd, efef, gg, is indeed the English sonnet. This poetic form, also known as the Shakespearean sonnet, is characterized by its structure that encompasses the three quatrains that often develop a theme or introduce a problem, followed by a couplet that delivers a resolution or a twist.

The rhyme scheme plays a crucial role in helping to create rhythm and enhance the musical quality of the poem. Each quatrain presents a fresh perspective or builds upon the previous stanza, leading to a conclusion in the final couplet. This makes the English sonnet distinct from other forms of poetry, which have different structures and rhyme schemes.

In contrast, ballads typically tell a story and often have simpler rhyme schemes and a refrain. Limericks are known for their humorous tone, specific AABBA rhyme scheme, and five lines, while Haikus focus on nature and adhere to a 5-7-5 syllabic structure. Thus, the defining characteristics of the English sonnet make it the clear answer in this case.