Food is a critical category of resources, responsible both for keeping your colonists alive and their morale (through food variety and quality). Food can be acquired either by farming the local area or importing large quantities of food from the colony ship.
Obviously, if you don't have enough food, morale and health suffers. A colony full of dead colonists or an unhappy one will kill your tenure.
Colonists consume about 0.1 to 0.2 units of food per capita. Having a good supply of food for winter is a crucial concern.
Wondering what the difference between alien and terran food is? Well, alien crops grow faster (check the growth multiplier when selecting crops to plant) and after processing can provide a bigger surplus of food (this is essential in Cerulean Vale).
All the foodstuffs that are directly consumable straight from the farm. Ration packs are the only exception, as they are edible as-is, but can only be obtained by trading with the colony ship.