Hunger is the sensation of needing — or wanting — to eat something. People use the same word to describe a hankering for a snack or for the more dire meaning of starvation, as in "world hunger."
Hunger sometimes refers to an extreme lack of food, the equivalent to starvation: "We need to do something about hunger in poor communities." It can also simply mean your afternoon craving: "My daily hunger for chocolate was distracting me from my work." You can also hunger for things, both food (like when you hunger for French fries) and non-food things (like when you hunger for attention).