Ambrosia

"The healing god food used in emergencies, when demigods are seriously hurt. Ambrosia will cure almost any injury, although too much can make a demigod feverish and kills mortals. At Camp Half-Blood ambrosia comes in squares in sealed bags. On Mount Olympus you can buy it on a stick."

- excerpt from The Ultimate Guide

In Greek mythology, Ambrosia was the food eaten by the gods, usually presented in small cubes. It gave immortality to whoever ate it (although not in the Percy Jackson universe). It is closely related to Nectar. Ambrosia was fed to wounded demigods to heal their injuries.

Percy Jackson and the Olympians
Ambrosia is used as healing food to be used when someone gets injured in battle. Demigods can consume it, but if they have too much it can make them feverish and mortals can't eat it at all. It takes the taste of the user's favorite foods.

The Lost Hero
Piper McLean eats part of an ambrosia square when she broke her foot after falling from Festus, saying that it tastes like black bean soup her dad, Tristan McLean, used to make for her when she was ill.

Consumption
Ambrosia is the food of the gods. It is also used for healing by demigods. If a mortal eats it, they would be incinerated. A demigod can eat a little, but taking an overdose could make them feverish. A huge overdose would cause them to incinerate as a mortal would. It is the flavor of what each demigod prefers. Like for Percy, it was warm chocolate chip cookies, while for Piper it was the black bean soup her father used to make her.