Serum is a clear, yellowish fluid that remains after blood has clotted. It contains water, electrolytes, proteins, hormones, and waste products. Unlike plasma, which includes clotting factors, serum is used in various medical tests and research because it provides valuable information about a person's health without the interference of clotting components. In laboratory settings, serum is often analyzed to measure levels of specific substances, such as glucose, cholesterol, and enzymes. This analysis helps in diagnosing conditions like diabetes, heart disease, and liver disorders. Additionally, serum can be used in the development of vaccines and therapies, making it an essential component in both clinical and research environments.