What exactly is meant by the "M4 corridor"?

Because the M4 goes into London, many people want to live with good access to it to travel into the City so the M4 corridor is basically any towns/villages with good access to the motorway. People think they are 'escaping to the country' out of London whereas all they are really doing is creating a lot of 'dead' towns, deserted during the working week except for bored 4x4 driving women.