What is the difference between reflection and incidence of exposure meter?

There are two photometry methods: incident and reflection. The incident exposure meter is used to measure the incident light intensity in front of the photographed object, and the reflection type is used to measure the light intensity reflected from the photographed object to the camera lens. The built-in exposure meter of the camera is reflective, and most hand-held exposure meters are dual-purpose. The milky white cover is used to switch between two metering methods.