What does iso photography mean?

Sensitivity, also known as ISO value, is a measure of the sensitivity of a film to light. It is determined by sensitivity measurement and measuring several numerical values. It has recently been standardized by the International Organization for Standardization. Extended information

For less sensitive films, a longer exposure time is required to achieve the same image as a more sensitive film, so it is often called a slow film. Highly sensitive films are therefore called fast films. Whether it is digital or film photography, using a higher sensitivity to reduce exposure time usually results in lower image quality (due to coarser film grain or higher image noise or other factors).