ISO refers to the sensitivity of a camera’s image sensor to light. The higher the ISO value, the more sensitive the sensor is to light, allowing you to capture images in low-light conditions without having to use a slower shutter speed or larger aperture.

In digital photography, ISO is usually represented as a numerical value, such as 100, 200, 400, 800, 1600, etc. Each step up in ISO doubles the sensor’s sensitivity to light. For example, an image taken at ISO 800 is twice as sensitive to light as an image taken at ISO 400.

However, increasing the ISO value also introduces digital noise or graininess to the image, which can reduce the overall image quality. So, it’s important to choose the appropriate ISO value depending on the lighting conditions and the desired effect for the image.

Low ISO values, such as ISO 100 or 200, are typically used in bright light conditions or when a low level of digital noise is desired. High ISO values, such as ISO 1600 or above, are used in low-light situations or when you need a faster shutter speed to freeze action.

Most digital cameras allow you to adjust the ISO setting manually, but some cameras also have an automatic ISO mode that adjusts the ISO value based on the lighting conditions.