Is msa a defined or an undefined medium provide the reasoning?

The Mannitol salt Agar is a undefined medium.

A chemically defined medium is a growth medium suitable for the vitro cell culture of human or animals in which all of the chemical components are known. MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. It is important in medical laboratories by distinguishing pathogenic microbes in a short period of time.