Cell culture media can be classified into two main categories, undefined and defined media.

• An undefined medium (also known as a complex medium or a basal medium) contains complex ingredients such as beef and yeast extract. The exact species and their amount present in the medium are unknown, hence “undefined”. This type of media is sometimes chosen because some microorganisms cannot be cultured on defined media.
• A defined medium (also known as chemically defined medium or synthetic medium), on the contrary, have known quantities of all ingredients. It is entirely free of animal-derived components, and represents the purest and most consistent cell culture environment.