Frenching is the act of recessing or moulding a headlight, taillight, antenna or number plate into a car body to give a smoother look to the vehicle.
Frenching a headlight or taillight is done in one of two ways: either removing the bezel, mounting the light deeper in the car's head or taillight nacelle and using the headlight rings from another car (or an aftermarket kit) to mount it deeper into the body.
This modification is seldom carried out on late models, as newer cars have flush-fitting headlights.
This is done by cutting an area of sheet metal in the shape of a number plate (for example), fabricating a box and welding it deeper into the body.
The same principle is used in recessing car radio antennas, only that a hole must be drilled into the bottom of the tubing to let water drain out, reducing the risk of corrosion.