An indicator is something that points to an issue or condition. Its purpose is to show you how well a system is working. If there is a problem, an indicator can help you determine what direction to take to address the issue.
Indicators are as varied as the types of systems they monitor.
Effective indicators are easy to understand , even by people who are not experts. An example of an indicator is the gas gauge in your car. The gas gauge shows you how much gasoline is left in your car. If the gauge shows the tank is almost empty, you know it's time to fill up. Another example of an indicator is a midterm report card.