Chocolate is a food item which provides a small amount of nutrition, filling a colonist's hunger meter by 10% per unit consumed. Unlike most other foods, it also grants a bonus to Joy of 10% per unit.
The low nutritional value and rarity of chocolate makes it a poor choice to try to sustain a colony with, but its joy-boosting properties make it excellent for keeping colonists' mood up.
Colonists will eat no more than 4 units of chocolate at a time, and won't touch it on their own unless they are desperate for food. Manually directing troubled colonists to eat it when necessary is advised.