What is a Mirrorless Camera?
In a Mirrorless cameras, light passes through the lens and right onto the image sensor, which captures a preview of the image to display on the rear screen. Some models also offer a second screen inside an electronic viewfinder that you can put your eye up to.

A mirrorless interchangeable-lens camera (MILC), frequently simply mirrorless camera, also called DSLM (digital single lens mirrorless), and sometimes also called EVIL (electronic viewfinder, interchangeable lens) features a single, removable lens and uses a digital display system rather than an optical viewfinder. The word “mirrorless” indicates that the camera does not have a reflex mirror or optical viewfinder like a conventional digital single-lens reflex camera (DSLR), but an electronic viewfinder which displays what the camera image sensor sees.^[1]

Many mirrorless cameras retain a mechanical shutter. Like a DSLR, an interchangeable-lens mirrorless camera accepts any of a series of interchangeable lenses compatible with the lens mount of that camera. A mirrorless interchangeable lens camera is an alternative to the digital single-lens reflex camera (DSLR).