In microbiology, a pure culture is a laboratory culture that contains a single species of organism, according to Encyclopædia Britannica. A pure culture is usually derived from a mixed culture.
A mixed culture is a culture that contains many species. The pure culture is derived from the mixed culture by transferring a small sample into a new sterile growth medium in a manner that disperses the individual cells across the medium's surface. It can also be derived by thinning the sample manifold before inoculating the new medium. Both methods separate the individual cells so that when the cells multiply, each cell forms a discrete colony. The cells may then be used to inoculate more media with the assurance that only one type of organism is present.