High ISO settings refer to the sensitivity of a camera's sensor to light. When you increase the ISO number, such as from ISO 100 to ISO 1600, the camera can capture images in lower light conditions without using a flash. This is particularly useful for indoor photography or nighttime scenes. However, using high ISO settings can introduce noise, which appears as grainy or speckled areas in the image. While modern cameras, like those from Canon or Nikon, have improved noise reduction technology, it's still important to balance ISO with other settings like aperture and shutter speed for optimal results.