Distance food was transported from being made to being eaten. Lower is better.
Food Miles is a the distances food traveled between in its journey from generation to consumption.
grown/slaughtered → prepared & packaged → consumed
The lower the number of average food miles of the food you eat, the lower the environmental impact of your eating.
From an energy perspective, the energy content of a grape doesn’t change depending on where it’s from and how far its come - but its net energy (it’s caloric energy minus its Embodied Energy) is very much affected.
It’s much more efficient to grow your own garden from seeds than it is to have all your food shipped in from farms afar.