What does Huawei mate8 professional camera iso mean?

ISO in Huawei mate8 camera means sensitivity value.

Sensitivity (ISO value) is a photographic concept in the film age. ISO (International Organization for Standardization) has formulated the speed standard of film chemical reaction to light, which is also the speed standard of film manufacturing industry. The higher the sensitivity, the faster the speed, but the picture quality is rough.

Extended data:

Sensitivity, also known as ISO value, is a measure of the sensitivity of negative film to light, which is determined by the measurement of sensitivity and several values, and has recently been standardized by the International Organization for Standardization. For the negative with low sensitivity, it takes a long exposure time to achieve the same imaging effect as the negative with high sensitivity, so it is usually called slow negative. Highly sensitive negatives are therefore called fast negatives. Whether it is digital or negative photography, in order to reduce exposure time, relatively high sensitivity usually leads to poor image quality (due to thick negative particles or high image noise or other factors).

References:

Baidu encyclopedia sensitivity