[count] 1 : an event or act which shows that something exists or that gives information about something : sign
▪ The change in his behavior is clearly a signal [=indication] that there is a problem. ▪ He likes her but he is sending the wrong signals with his constant teasing. — often + of ▪ Inflammation is a signal of infection. 2 : something (such as a sound, a movement of part of the body, or an object) that gives information about something or that tells someone to do something
▪ Don't start until I give the signal. [=sign] ▪ The teacher gave us the signal to finish what we were working on and hand in our tests. ▪ The pilot sent out a distress signal [=a message that the airplane was in danger] before the plane crashed. ▪ They communicated with each other by using hand signals. [=movements of a person's hands that mean something] 3 : a piece of equipment with colored lights that is used on railways and roads to tell people when to go, to slow down, or to stop
▪ Faulty wiring in the train station caused a signal to malfunction. ▪ The traffic signal [=traffic light] was not working. 4 technical a : a message, sound, or image that is carried by waves of light or sound
▪ The video/TV signal is scrambled. ▪ Satellite dishes receive television signals. ▪ a digital signal ▪ The transmitter beams radio signals into space.
b : a wave of light or sound that carries a message, sound, or image
▪ We'll need better equipment to generate a 50 Hz signal.