In photography, the iso, aperture, and shutter speed are the three main settings that determine the exposure of a photograph.
Iso refers to the sensitivity of the camera's image sensor to light. A lower iso value means that the sensor is less sensitive to light, while a higher iso value means that it is more sensitive to light. A higher iso value can be useful in low light situations, but can also result in image noise (graininess) in the photo.
Aperture is a measure of the size of the opening in the lens through which light enters the camera. A wider aperture (a smaller f-number) lets in more light and creates a shallower depth of field (less of the photo is in focus), while a narrower aperture (a larger f-number) lets in less light and creates a deeper depth of field (more of the photo is in focus).
Shutter speed refers to the amount of time that the camera's shutter is open, allowing light to reach the image sensor. A faster shutter speed means that the shutter is open for a shorter amount of time, which can freeze fast-moving subjects and reduce motion blur. A slower shutter speed means that the shutter is open for a longer amount of time, which can create motion blur and is useful in low light situations.
Together, these three settings determine the exposure of a photograph and allow the photographer to control the amount of light and the visual effects in the final image.