Selective media are types of growth media used in microbiology that allow certain types of microorganisms to grow while inhibiting others. This is achieved by adding specific nutrients or inhibitors that favor the growth of desired organisms, such as bacteria or fungi, while suppressing unwanted species. These media are essential for isolating and identifying specific microorganisms in a mixed sample. For example, MacConkey agar is a selective medium that allows gram-negative bacteria to grow while inhibiting gram-positive bacteria, making it easier to study and analyze the characteristics of the target organisms.