An amino acid is often times called a residue, so a n-residue polypeptide segment translates to n-amino acid polypeptide chain. It is pretty clear, I'm not sure what's confusing you. What did the Google search reveal?

A 13 residue polypeptide is a short sequence of amino acids. This might be part of a larger protein, or could just be a peptide by itself.

A residue is another name for a single amino acid within a protein or peptide.

That's all I can say about your question at the moment because it lacks content. I have no idea what a segment pair means, nor what context this is meant to be in.

Please clarify your question, especially how it relates to bioinformatics (just tagging bioinformatics doesn't make it a bioinformatics question), else we may close it.