Selective agar is a type of growth medium used in microbiology to isolate specific types of bacteria while inhibiting the growth of others. This is achieved by adding certain chemicals or nutrients that favor the growth of the target organisms, making it easier to study their characteristics and behaviors. Common examples of selective agar include Mannitol Salt Agar, which is used to isolate Staphylococcus species, and MacConkey Agar, which is designed for the differentiation of Gram-negative bacteria. By using selective agar, researchers can effectively identify and analyze specific microbial populations in various samples.