To watch by craning the neck (as though it were made of rubber), especially if the observer and observed are in motion relative to each other.
The driver was so busy rubbernecking, trying to get a good view of the accident, that he was almost part of another accident.
The act of slowing down whilst driving a vehicle, in order to see the scene of an accident.
Generally, any act of observation in a manner considered unduly overt or otherwise unseemly.
The children had never been in such a large museum and their rubbernecking was rather amusing.