About:
Freeze-drying, or lyophilization, is like "suspended animation" for food. In this process, fresh or cooked food is rapidly frozen and placed in a vacuum.
Virtually any food item and ingredient can be freeze-dried. To do this however, specialized equipment is required, making it a costly option.
Cell structure, nutrients, shape, and color are all preserved because of this rapid change, allowing the food to keep a ÒfreshÓ look and nutrition.
When it is added to boiling water, freeze-dried food can reconstitute in only a few minutes.

Freeze-drying may keep the food's original look, but it takes up substantially more room than compact dehydrated food.

Dehydrated, or dried, food is made by applying heat to the desired food item, resulting in 98% of the substance's water being lost to evaporation.
This technique has been performed, though through different methods (air drying, sun drying, etc.), for years to preserve foods.

Source: Freeze-drying & Dehydration at Wild Backpacker

	Freeze-dried Food	Dehydrated Food
Weight Reduction	✓	✓
Nutritional Content	✓✓	✓
Space Savings	✓	✓✓
Taste	✓✓	✓
Cost	$$$	$
Rehydration	5 min. in boiling/hot water; 5-10 min. in cold water	1-2 hours in cold water; 5-20 min. in boiling water

From Packit Gourmet via Wild Backpacker

Dehydrated food:
Air Dried Vegetables at NorthBayTrading.com
Dehydrated Vegetables | HarmonyHouseFoods.com
Dehydrated Vegetables & Freeze Dried Meat at BackPackingChef.com

Freeze Dried:
Freeze-Dried Food at REI
Eastern Mountain Sports
MOUNTAIN HOUSE: Standup Pouch: Main Entrees

Links:
Dehydrated Food vs. Freeze Dried Food