Jealousy generally refers to the thoughts or feelings of insecurity, fear, and concern over a relative lack of possessions or safety.

Jealousy can consist of one or more emotions such as anger, resentment, inadequacy, helplessness or disgust. In its original meaning, jealousy is distinct from envy, though the two terms have popularly become synonymous in the English language, with jealousy now also taking on the definition originally used for envy alone. These two emotions are often confused with each other, since they tend to appear in the same situation.

Jealousy is a typical experience in human relationships, and it has been observed in infants as young as five months. Some researchers claim that jealousy is seen in all cultures and is a universal trait. However, others claim jealousy is a culture-specific emotion.

Jealousy can either be suspicious or reactive, and it is often reinforced as a series of particularly strong emotions and constructed as a universal human experience. Psychologists have proposed several models to study the processes underlying jealousy and have identified factors that result in jealousy. Sociologists have demonstrated that cultural beliefs and values play an important role in determining what triggers jealousy and what constitutes socially acceptable expressions of jealousy. Biologists have identified factors that may unconsciously influence the expression of jealousy.

Throughout history, artists have also explored the theme of jealousy in paintings, films, songs, plays, poems, and books, and theologians have offered religious views of jealousy based on the scriptures of their respective faiths.