This came to prominence when the Duke of Edinburgh drove straight into another car in a T intersection. There had been a few instances of it in Australia before that. The more formal name is side impact collision or broadside accident. This new name provides a visual reference that is arresting, so to speak. One vehicle travelling along the centre line of the T crashes into the side of the vehicle travelling along the top, usually because the driver has failed to stop at lights or give way at a stop sign. I suppose this might have been termed simply T-crash, which is geometrically accurate but somewhat abstract. T-bone crash adds the necessary visceral juiciness. This kind of accident is inherently more dangerous than most because the car door offers very little protection for the people being T-boned.
The T-bone crash has given rise to the verb to T-bone as in to T-bone a car, to T-bone someone, a T-boned car. There is considerable variation in the spelling, sometimes with a capital T, sometimes a lowercase t.