signal
n//ˈsɪɡnəl//signal
A sign made to give notice of some occurrence, command, or danger, or to indicate the start of a concerted action.
An on-off light, semaphore, or other device used to give an indication to another person.
(of a radio, TV, telephone, internet, etc.) An electromagnetic action, normally a voltage that is a function of time, that conveys the information of the radio or TV program or of communication with another party.