These four words get thrown around interchangeably, but they describe very different processes and very different snacks.
Freeze-dried: Fruit or corn is frozen, then dried in a vacuum using sublimation. No heat, no oil. Result: light, crunchy, airy texture with high nutrient retention and a long natural shelf life because there's almost no moisture left for bacteria or mold to grow.
Dehydrated: Fruit is dried slowly using low heat over many hours (think sun-drying or a low-temperature oven/dehydrator). Result: a chewy, leathery texture. Some nutrients are lost to heat, and because dehydrated fruit retains more moisture, many brands add sulphur dioxide or other preservatives to stop it from spoiling and often sugar to balance out the tartness that develops.
Fried: Fruit, vegetables, or corn are cooked in hot oil. Result: crispy texture, but with significant oil absorption, loss of heat-sensitive nutrients, and the formation of compounds like acrylamide at high temperatures. Shelf life is short unless preservatives are added.
Baked: Cooked dry in an oven. Often marketed as the "healthy" alternative to frying, but many baked snacks still contain added oils, salt, and sugar to make up for the flavor lost in cooking and the high, sustained heat still degrades nutrients.
The short version: freeze-drying is the only one of these four methods that uses neither heat nor oil, which is precisely why it can produce a genuinely crunchy snack without frying or baking.