Final answer:
The correct term for the pause or break within a line of Middle English alliterative meter is a caesura, which is used to add emphasis and rhythmic variety.
Step-by-step explanation:
In Middle English alliterative meter, the two half-lines are separated by a pause or break known as the caesura.
This stylistic device is used by poets to add emphasis or to create a particular rhythmic effect within a line.
A caesura is not to be confused with a line break, where the line ends completely, or enjambment, where a sentence or phrase runs over from one line to the next without a terminal punctuation mark.
Unlike end rhymes, which occur at the end of lines, or a split couplet, which employs two rhyming lines of different lengths, a caesura interrupts the flow within a single line.