An ARM's-length portrait is a type of self-portrait, usually taken with a camera or smartphone. It is typically taken from a distance, with the photographer standing at ARM's length away from the camera. This type of portrait is often used to capture a moment in time, or to document a person's physical appearance. The term 'ARM's-length portrait' is derived from the idea that the photographer is standing at ARM's length away from the camera, creating a more natural and relaxed pose.