You know those old movies when somebody manually cranks the aeroplane propeller and yells 'Contact", well what does that mean?

Maybe for the person in the pilot's seat to then turn the ignition switch to "on". If it's turned on too soon, it could possibly burn out the spark plug, or electrical system or whatever they had back then. That's my guess. My first husband and my dad are both pilots, but of glider planes only.

The word "contact" is used to signify from the person cranking the propeller that the magneto (ignition) switch should be set to "on." After the seat person (pilot) turns the switch on, he will yell "contact" to the propeller person to let him know that he has, indeed, turned the magneto's switch to "on." If the front man wants the switch turned off, he will yell "switch off," and the seat man will reply the same when he does so. All of this is for safety reasons. Under noisy conditions "switch on" and "switch off" could sound very much the same, and someone could be seriously hurt or killed, and so "contact" is used because it both accuratetly describes the condition of the ignition, and it sounds nothing at all like "switch off."