N-terminal end

The N-terminal end (also known as the N-terminus, N-terminal domain or amine-terminus) refers to the extremity of a protein or polypeptide terminated by an amino acid with a free amine group (-NH2).

Chemistry
Each amino acid has a carboxyl group and an amine group, and amino acids link to one another to form a chain by a dehydration reaction by joining the amine group of one amino acid to the carboxyl group of the next. Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an amine group, the N-terminus.

The convention for writing peptide sequences is to put the N-terminal end on the left.