Incident light is the light falling on a subject.
An incident light meter placed close to the subject reads the ambient light that is falling on the subject, so the meter is sometimes called an incident light meter and sometimes called an ambient light meter. In either case, it reads the light that is actually there, striking your subject. Reflected light is the light reflected by your subject. The light meters in most popular cameras read reflected light, but with a little addition they can also be made to read incident light. This simulates an incident light meter's translucent cap, enabling your camera's meter to read the incident light.