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 Recreation of 10% per unit.
Chocolate's low nutritional value makes it a poor choice to try to sustain a colony with, but its recreation-boosting properties make it excellent for keeping colonists' mood up.
Colonists will eat no more than 4 units of chocolate at a time. Manually directing troubled colonists to eat it when necessary is advised.
Chocolate can be acquired by planting cocoa trees, making chocolate good for selling or improving colonists' moods. They can also be purchased from bulk goods traders, or occasionally arrive in cargo pods.
In Beta 18 or earlier, chocolate could not be produced by your colonists, and was exclusively a trade good.