Explain Complex or Undefined Media?

Here, the exact composition of the medium is not known. It contains some complex components of plant and animal extracts whose exact chemical composition is not known. For example, undefined components, like, peptone, beef extract, yeast extract etc. may be present in complex media. These are useful because

(i) Many microorganisms can grow on the same media, and

(ii) It can be used when nutritional requirement of a particular microorganism is unknown.

Example: yeast extract broth, nutrient broth, potato dextrose agar etc.