The movie Traffic tells me that ‘traffic’ means to trade or deal in a commodity or service (definition). Did the police man make a ‘traffic’ stop? Not if I’m not trading or dealing in goods. They call it a traffic stop to convert traveling into a commercial activity, called trafficking, they can then regulate. Trafficking is not just about drugs or humans; it’s trading or dealing in any goods.
Similar words that are turned into terms and are abused in everyday language are ‘driving’ and ‘passenger’.
Am I driving? Not if I’m not for hire.
Do I have passengers? Not if I’m not for hire and not if they’re not also paying me.