In photography, a strong subject refers to a main element or point of interest in an image that immediately catches the viewer's attention. It is the focal point of the composition, and often the reason why the photographer chose to take the photo in the first place. 

A strong subject can be a person, object, landscape, or any other element that stands out in the frame. It should be visually compelling and have a clear relationship with the other elements in the image. 

A strong subject can create a sense of balance, contrast, or emotion in the photograph, and can guide the viewer's eye through the composition. Capturing a strong subject often requires careful composition and attention to detail, as well as an understanding of lighting, color, and other technical aspects of photography.