Incident-light Metering
Measuring the light falling onto a subject rather than the light reflecting off it, using a handheld meter with a white diffusing dome.
Measured in
EV
In depth
Because it ignores the subject's tone entirely, incident metering returns the same reading for a black cat and a white cat, and both will render correctly. It requires physically standing at the subject and pointing the dome back toward the camera, which is why it belongs to studio, portrait and cinema work rather than reportage.
Examples in practice
A studio photographer meters incident at the model's chin, sets f/8 on the camera, and shoots black and white outfits without touching the exposure.