High ISO performance refers to a camera's ability to capture clear images in low-light conditions by increasing the sensitivity of its sensor. When the ISO setting is raised, the camera can detect more light, allowing for better exposure without using a flash. However, higher ISO settings can introduce noise, which appears as graininess in the image. Modern cameras, especially those from brands like Canon, Nikon, and Sony, have improved high ISO performance, enabling photographers to shoot in darker environments with less noise. This advancement is particularly beneficial for genres like night photography and wildlife photography, where lighting conditions can be challenging.