What does it mean when a car vibrates shudders with the headlights on only in drive or reverse and only when sitting?

I'm guessing it's an older car (as in at least 5 or more years, or a lot of miles). over time, the brackets that hold the motor to the chassis begin to wear, and the engine vibration becomes more apparent inside the car. this is made worse when you put more of a load on the engine by requiring it to power the headlights or engage the transmission.