What does warning light with waves under it on dashboard mean?

If it is a car with waves under it then it is a slip indicator. If it is just waves it can be low coolant or low windshield fluid. It can also be rear defroster indicator. Need better description and make, model, and year of vehicle to be sure.
If it is a car with waves under it then it is a slip indicator. If it is just waves it can be low coolant or low windshield fluid. It can also be rear defroster indicator. Need better description and make, model, and year of vehicle to be sure.