A quatrain is a stanza consisting of four lines.
The lines may have a variety of rhyming schemes such as: aabb (a double couplet), abba (an envelope quatrain), abab (an alternating quatrain), and the like.
Normally, the quatrain is written as a self contained poetic piece; however, it may be written as one stanza in a series of others.
A couplet is a pair of rhymed lines that may or may not constitute a separate stanza verses to craft a poem.
The couplet may be rhymed or unrhymed.
One will note that the Shakespearian sonnet always ends with a rhymed couplet.
The following poem regarding 911 takes the quatrain and the couplet forms; integrate the two, thus producing a rhyming couplet quatrain poem.
911 - A Resolve Strengthening Liberty: The message read-"Pack your duffel bag!" It was very heavy; across the floor it was dragged; A second thought did not cross my mind Leaving home with a vision to help humankind; Seeing justice served upon those responsible Pondering how could others be-"so irresponsible?" I did not hesitate and moved in a quickened pace The sense of urgency was quickly embraced; Motivating many to do their best Some fought and met the ultimate test; Nine-one-one has bled in many hearts For their missing loved one in many parts; Yellows ribbons still wrapped around many trees While families are still on their bended knees; A day that is never to be forgotten Many prayed for their loved ones now in heaven; Returning home sometimes I cried Especially for the innocent ones just passing by; With faith we continue to grow While our resolve of liberty the world will know!