It is a rhyme scheme not scheem. It means rhyming of two words that fall at the end of verses such as;
Bid me weep and weep,
When there is nothing to keep.
Here “weep” and “keep” rhyme with each other. This is called rhyme and will be denoted with A. Similarly, next rhymes with be denoted with B or C and so on.
English Tutor Answered question May 3, 2020