Food security is the state of having reliable access to a sufficient quantity of affordable, healthy food. The availability of food for people of any class, gender, ethnicity, or religion is another element of food protection. Similarly, household food security is considered to exist when all the members of a family have consistent access to enough food for an active, healthy life. Food-secure individuals do not live in hunger or fear of starvation. Food security includes resilience to future disruptions of food supply. Such a disruption could occur due to various risk factors such as droughts and floods, shipping disruptions, fuel shortages, economic instability, and wars. Food insecurity is the opposite of food security: a state where there is only limited or uncertain availability of suitable food.

The concept of food security has evolved over time. The four pillars of food security include availability, access, utilization, and stability. In addition, there are two more dimensions that are important: agency and sustainability. These six dimensions of food security are reinforced in conceptual and legal understandings of the right to food. The World Food Summit in 1996 declared that "food should not be used as an instrument for political and economic pressure."

There are many causes of food insecurity. The most important ones are high food prices and disruptions in global food supplies for example due to war. There is also climate change, water scarcity, land degradation, agricultural diseases, pandemics and disease outbreaks that can all lead to food insecurity. Additionally, food insecurity affects individuals with low socioeconomic status, affects the health of a population on an individual level, and causes divisions in interpersonal relationships. Food insecurity due to unemployment causes a higher rate of poverty.

The effects of food insecurity can include hunger and even famines. Chronic food insecurity translates into a high degree of vulnerability to hunger and famine. Chronic hunger and malnutrition in childhood can lead to stunted growth of children. Once stunting has occurred, improved nutritional intake after the age of about two years is unable to reverse the damage. Severe malnutrition in early childhood often leads to defects in cognitive development.

Food security, as defined by the World Food Summit in 1996, is "when all people, at all times, have physical and economic access to "sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life".

Food insecurity, on the other hand, as defined by the United States Department of Agriculture (USDA), is a situation of "limited or uncertain availability of nutritionally adequate and safe foods or limited or uncertain ability to acquire acceptable foods in socially acceptable ways."

At the 1974 World Food Conference, the term food security was defined with an emphasis on supply; it was defined as the "availability at all times of adequate, nourishing, diverse, balanced and moderate world food supplies of basic foodstuffs to sustain a steady expansion of food consumption and to offset the fluctuations in production and prices." Later definitions added demand and access issues to the definition. The first World Food Summit, held in 1996, stated that food security "exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life."

Chronic (or permanent) food insecurity is defined as the long-term, persistent lack of adequate food. In this case, households are constantly at risk of being unable to acquire food to meet the needs of all members. Chronic and transitory food insecurity are linked since the recurrence of transitory food security can make households more vulnerable to chronic food insecurity.