In real estate photography, ISO refers to the sensitivity of the camera's image sensor to light. It is an essential setting to consider when dealing with different lighting conditions.  A higher ISO value increases the sensor's sensitivity, allowing you to capture images in low-light situations. However, higher ISO settings can introduce noise or graininess in the image.  Maintaining image quality is generally recommended to keep the ISO as low as possible while maintaining proper exposure.  Real estate photographers often strive for clean and noise-free images, so finding the optimal ISO setting based on the available light is crucial.