The main difference between freeze drying and dehydrating food is how moisture is removed from the food. Freeze drying uses a vacuum to sublime the moisture from the food. Dehydration uses heat to remove moisture.
Freeze drying costs more and takes much longer, but it maintains more of the food’s nutrients, flavor, and shape.
Dehydrating food is much cheaper and quicker, but it also doesn’t completely dry the food and it changes the food’s shape, flavor, and nutrients.