An Enclosed Rhyme is a type of poem that features a rhyming scheme that is often found in literature in the form of "ABBA". This means that the first line of the poem and the fourth line of the poem make a rhyme together; Similarly, the second line of the poem and the third line of the poem make a rhyme together as well. In any case, an enclosed rhyme an introverted quatrain, or rather a stanza, as the rhyming lines are in a varying order as opposed to what is normally seen in a complete poem of four lines.
Enclosed rhymes, or enclosing rhymes as also known, can take many forms. An excellent example of this format is featured in Wilfred Owen's "Exposure". This particular piece shows the enclosed rhyming structure throughout each of the eight stanzas that make up the poem itself. Another example of this structure can be found in the very first verse or stanza of Matthew Arnold's piece entitled "Shakespeare".
The rhyme scheme "abba" (that is, where the first and fourth lines, and the second and third lines rhyme).
Example
How soon hath Time, the subtle thief of youth,
Stolen on his wing my three and twentieth year!
My hasting days fly on with full career,
But my late spring no bud or blossom shew'th.
(From John Milton's "On His Being Arrived to the Age of Twenty-Three")