A Petri dish is a shallow, flat, cylindrical container made of glass or plastic, commonly used in laboratories for growing cultures of microorganisms. It typically has a lid that covers the dish to prevent contamination. The dish is filled with a nutrient-rich gel called agar, which provides a suitable environment for bacteria, fungi, and other cells to grow. These dishes are essential tools in microbiology and are used for various experiments, including testing the effects of antibiotics or studying the growth patterns of different organisms. The design allows for easy observation and manipulation of the cultures, making it a fundamental item in scientific research.