a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time
"The rising unemployment rate serves as an early indicator that the economy is slowing down."
a signal for attracting attention
"The flashing red light served as an indicator to warn drivers that the pedestrian crossing was about to activate."
a device for showing the operating condition of some system
"The dashboard indicator lit up red to warn that the car's oil pressure had dropped too low."
(chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction
"The teacher added phenolphthalein as an indicator to show when the titration reached its endpoint."
A pointer or index that indicates something.
"The dashboard light serves as a clear indicator that the fuel tank is nearly empty."
In plain English: An indicator is a sign that shows what is happening or will happen.
"The dashboard indicator light turned red to warn the driver that the brakes needed repair."
Usage: Use "indicator" to describe a device or signal that shows the status or direction of something, such as a dashboard gauge or a sign pointing the way. It specifically refers to the tool that provides information about a condition rather than the thing being measured itself.
The word indicator comes from the Late Latin term indicātor, which literally means "one who points out." It entered English through its root verb indicate, retaining the original sense of someone or something that shows or signals information.