It is one of the three metering settings in a camera. Multi-zone metering is probably a default one in every camera. It calculates the exposure based on measurements of light levels over many small parts of the frame. It uses an algorithm that decides what the exposure should be based on different parameters that are coming from the data that the algorithm has been trained on. Every camera has their own algorithm, so it will differ between systems.
When to use multi-zone metering
Multi zone metering is useful for landscape photography, street photography or any situation where the light is not harsh/contransty.