Radiator fluid, also known as coolant, is a special liquid that helps to keep your car engine cool. It flows through the radiator and absorbs heat from the engine, preventing it from overheating. Full definition
Once you've removed the coolant level sensor and the coolant is done leaking, clean this area of loose radiator fluid, dirt, and other debris. (yourmechanic.com)
This sensor measures the level of coolant inside the radiator when it is cool; as warm or hot radiator fluid will expand as it heats. (yourmechanic.com)