What does the parameter iso f2.5 of photography mean?

Iso refers to sensitivity. The greater the sensitivity value, the worse the corresponding image quality, and the smaller the value, the better the image quality. F refers to the aperture, which can control the amount of light entering. The smaller the aperture value, the larger the actual aperture and the more incident light, and vice versa. For example, the aperture of f2.8 is larger than that of f3.5.