(1) The ideal backpacking food — lightweight and low volume. And expensive.
(2) Food that has been dried. Removing the water preserves the food and reduces its weight.
(1) Dehydrated food will make you explode if you eat it dry and then drink lots of water. Go ahead — try it and see.
(2) I'm more dehydrated than my food is, but it's still good to eat and I'm not.