Here's why:
* AABB rhyme scheme: The "AABB" refers to the rhyme scheme where the first and second lines rhyme, and the third and fourth lines rhyme. This creates pairs of rhyming lines, which are called couplets.
* Couplets in poetry: A couplet is a pair of lines that rhyme and usually have the same meter. They can be part of a longer poem or stand alone as a complete poem.
So, a poem with an AABB rhyme scheme can be called a couplet poem, or simply a couplet if it's only two lines long.