The phrase "low coolant level" refers to a condition where there is not enough coolant (also known as antifreeze) in the radiator or engine cooling system. Coolant is an essential component of the cooling system, which helps maintain optimal operating temperature for the vehicle's engine by absorbing and dissipating heat. When the level of coolant falls below the minimum mark on the reservoir tank, it indicates that there may not be enough coolant to effectively transfer and dissipate heat from the engine, leading to overheating or other potential issues. This condition should be addressed promptly by checking for leaks, adding more coolant if necessary, and ensuring that the cooling system is functioning properly.