Which characteristic defines a DSLR camera?

A DSLR, or Digital Single-Lens Reflex camera, is uniquely identified by its use of a movable mirror system that enables the photographer to directly view the scene through the lens. This characteristic allows for real-time composition, which is a standout feature of DSLR cameras compared to other types of cameras. The movable mirror reflects light from the lens up into an optical viewfinder, allowing the user to see exactly what the lens sees, which is crucial for accurate framing and focus.

In contrast, other types of cameras may not provide this direct viewing experience. Options that mention features such as a fixed lens or not using electronic sensors do not align with the essential definition of a DSLR. Similarly, while some DSLRs can be relatively lightweight compared to other camera systems, their defining characteristic lies firmly in the mirror mechanism that allows for direct viewing through the lens.