Definition
A small panel-mounted light that illuminates to show the status of a system or to alert the pilot to a specific condition, such as an alternator or generator failure, low voltage, gear position, or activation of a particular system.
Plain English
A little light on the instrument panel that turns on to tell you something about how a system is working — for example, that something has failed or that a switch is on.
Context Anchor
Seen on the instrument panel or warning-light panel during normal system checks and during alternator or generator failure procedures.
Derivation
Indicator comes from the Latin indicare, meaning “to point out” or “to make known.” That fits the aviation meaning because the light points out a system condition the pilot needs to notice.
Why Pilots Care
Provides immediate visual alert to critical failures so the pilot can take corrective action before power or other systems are lost.
Analogy
It is like the battery warning light on a car dashboard: the light is not the problem itself, but it tells you a system needs attention.
Intuition Check
Do not think of an indicator light as a light used to see in the cockpit. In this context, it is a message light: its job is to show the condition of a system.
Example Sentence 1
When the alternator failed, the low-voltage indicator light on the panel illuminated, prompting the pilot to begin the failure checklist.
Example Sentence 2
During the preflight check the pilot confirmed that no indicator lights were illuminated before engine start.