The main difference between Couplet and Quatrain is that the Couplet is a pair of lines of metre in poetry; two line stanza making complete sense and Quatrain is a type of stanza, or a complete poem, consisting of four lines
A couplet is a pair of successive lines of metre in poetry. A couplet usually consists of two successive lines that rhyme and have the same metre. A couplet may be formal (closed) or run-on (open). In a formal (or closed) couplet, each of the two lines is end-stopped, implying that there is a grammatical pause at the end of a line of verse. In a run-on (or open) couplet, the meaning of the first line continues to the second.
A quatrain is a type of stanza, or a complete poem, consisting of four lines.
Existing in a variety of forms, the quatrain appears in poems from the poetic traditions of various ancient civilizations including Ancient India, Ancient Greece, Ancient Rome, and China, and continues into the 21st century, where it is seen in works published in many languages. During Europe’s Dark Ages, in the Middle East and especially Iran, polymath poets such as Omar Khayyam continued to popularize this form of poetry, also known as Ruba’i, well beyond their borders and time. Michel de Nostredame (Nostradamus) used the quatrain form to deliver his famous prophecies in the 16th century.
There are fifteen possible rhyme schemes, but the most traditional and common are: AAAA, ABAB, and ABBA.
A rhyming end words.
A pair of one-way streets which carry opposing directions of traffic through gridded urban areas.
“5th Street is one-way west only and 6th Street is one-way east only. Together, they form a couplet in Downtown Los Angeles.”
A pair of two mutually exclusive choices in a dichotomous key.
A poem in four lines.
A stanza of four lines.
“Awake! for Morning in the Bowl of Night,”
“Has flung the Stone that puts the stars to flight:”
“And Lo! the Hunter of the East has caught”
“The Sultan’s Turret in a Noose of light.”