Biosafety Level (BSL) refers to a set of containment precautions required to isolate dangerous biological agents in a laboratory setting. There are four levels, ranging from BSL-1, which deals with well-characterized agents that pose minimal risk, to BSL-4, which involves highly dangerous pathogens that can cause severe or fatal diseases in humans. Each level has specific safety protocols, equipment, and facility designs to protect laboratory personnel and the environment. The classification of a biological agent into a specific BSL is based on its pathogenicity, mode of transmission, and the severity of the disease it causes. For example, BSL-2 is used for agents that can cause mild to moderate illness, while BSL-3 is for those that can lead to serious or potentially lethal diseases. Understanding these levels helps ensure proper safety measures are in place to prevent accidental exposure or release of harmful microorganisms.