A "tracer" is a substance or device used to track the movement of materials or processes. In scientific research, tracers can be radioactive isotopes or fluorescent dyes that help visualize the flow of fluids in biological or environmental studies. They are essential in understanding complex systems, such as how pollutants spread in water. In technology, a tracer can refer to a tool that monitors the path of data packets in computer networks. This helps identify issues in connectivity and performance. Tracers are crucial for both scientific investigations and troubleshooting in various fields, including biology, environmental science, and information technology.