The decisive moment is a concept popularized by the French photographer Henri Cartier-Bresson, who is considered one of the greatest photographers of the 20th century. Cartier-Bresson used the term to describe the split second when the elements in a scene come together perfectly to capture the essence of the moment, resulting in a powerful and evocative image.

According to Cartier-Bresson, the decisive moment is the point at which the photographer recognizes and captures the peak of action, emotion, or expression in a scene. This moment can be fleeting and requires the photographer to have a keen eye and the ability to anticipate and react quickly.

In 1952, Cartier-Bresson published a book entitled 'The Decisive Moment', which contained a collection of his photographs that captured these crucial moments. The concept has had a lasting impact on the field of photography, influencing generations of photographers and shaping the way we think about capturing and interpreting moments in time through images.