A camera monitor (or external monitor) is a monitor that attaches externally to a digital camera to aid with photography and cinematography. Camera monitors typically have larger displays than the built-in monitors on consumer cameras, and are also usually brighter and able to reproduce color better. Consumer friendly units use HDMI for connecting to the camera, while higher end camera monitors may also offer SDI connections.
While some are powered by a single battery, others can be powered by two batteries and offer a hot swapping capability. It's not uncommon for an AC adapter to be available as well for indoor photography or filming.