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.
"Exposure", by Wilfred Owen, also has an example of enclosed rhyme. Each of the eight stanzas have the ABBA half rhyming sequence: