World hunger refers to the second definition, aggregated to the world level. The related technical term (in this case operationalized in medicine) is either malnutrition, or, if malnutrition is taken to refer to both undernutrition and overnutrition, undernutrition. Both malnutrition and undernutrition refer to not having enough food.
Poverty is the principal cause of hunger.
Harmful economic systems are the principal cause of poverty and hunger
Climate change Climate change is increasingly viewed as a current and future cause of hunger and poverty.