The Viewfinder is the eyepiece on a camera that you hold close to your eye, to allow you to see what’s being photographed.
There are two types of viewfinders – optical, and digital.
An optical viewfinder in a DSLR works by light passing through the lens and bouncing off the reflex mirror and prism in your camera.
A digital, or electronic, viewfinder is a real time view of what the camera’s imaging sensor is seeing. Electronic viewfinders might be fitted to compact and mirrorless cameras, and are essentially exactly the same as what the LCD Live View screen shows.