A protein chain can be called several things, depending on the context:

* Polypeptide: This is the most common and general term, referring to a linear chain of amino acids linked by peptide bonds.

* Peptide: This term is often used interchangeably with polypeptide, but it can also refer to shorter chains of amino acids.

* Primary structure: This refers to the specific sequence of amino acids in the protein chain, which is crucial for its function.

So, while "polypeptide" is the most accurate and widely used term, "peptide" and "primary structure" can also be used to describe a protein chain, albeit with slightly different meanings.