A Geiger-Müller counter is a device used to detect and measure ionizing radiation, such as alpha particles, beta particles, and gamma rays. It consists of a Geiger-Müller tube filled with gas that becomes ionized when radiation passes through it. This ionization creates an electrical pulse, which is counted and displayed, indicating the level of radiation present. These counters are commonly used in various fields, including nuclear industry, environmental monitoring, and medical applications. They help ensure safety by measuring radiation levels in areas where exposure could be harmful, making them essential tools for professionals working with radioactive materials or in radiation-prone environments.