Enclosed rhyme (or enclosing rhyme) is the rhyme scheme "abba" (that is, where the first and fourth lines, and the second and third lines rhyme). Enclosed-rhyme quatrains are used in introverted quatrains, as in the first two stanzas of Petrarchan sonnets.
Example
How soon hath Time, the subtle thief of youth, A Stolen on his wing my three and twentieth year! B My hasting days fly on with full career, B But my late spring no bud or blossom shew'th. AExposure, by Wilfred Owen, also has a good example of enclosed rhyme. Each of the eight stanzas have the ABBA half rhyming sequence:
Our brains ache in the merciless iced east winds that knive (A us ... A) Wearied we keep awake because the night is silent ... (B) Low, drooping flares confuse our memories of the salient ... (B) Worried by silence, sentries whisper, curious, nervous, (A) But nothing happens.
References
Enclosed rhyme Wikipedia(Text) CC BY-SA