It means you most likely have a faulty thermostat. Does it take a while for your car to get to operating temp? Your temperature should get to 190 within about 2 to 3 miles of startup and never drop below 190 for the duration of your trip. Is this how your car operates? Also check the color of the coolant temperature sensor which is on the side of the cylinder head in the coolant flange if you have a 4 cylinder. If the sensor is black or green with a yellow dot those sensors have known issues and should be replaced to prevent future issues. If it's just a green sensor then I wouldn't mess with it.