Amino acids are divided into two groups, essential amino acids and nonessential amino acids. Nonessential amino acids can be made or constructed by the body whereas essential amino acids need to be added to a diet in order for the body to have them.
A polymer formed of amino acids is a polypeptide (named from the numerous peptide bonds in the chain; one peptide bond links two amino acids). Two amino acids joined form a dipeptide, hundreds of amino acids form a polypeptide.
Several amino acids are not coded for in biology. 20 are. The two standard amino acids are selenocysteine and pyrrolysine. Then there are the numerous non-standard amino acids, which include hydroxyproline and selenomethionine.
The bond between two amino acids is called a peptide bond. Any length of amino acids strung together by peptide bonds is called, generally, a peptide. Two amino acids held together by a peptide bond is called a dipeptide.