To differentiate that role from that of "key" modeling when a modeling source moves behind the object, it is typically called a "rim" or "accent" light. In portrait lighting, it also called a "hair" light because it is used to create the appearance of physical separation between the subject's head and background.
Creating Natural Looking Artificial Lighting
A typical studio lighting configuration will consist of a fill source to control shadow tone, a single frontal key light to create the highlight modeling clues on the front of the object facing the camera over the shadows the fill illuminates, one or more rim/accent lights to create separation between foreground and background, and one or more background lights to control the tone of the background and separation between it and the foreground.
There are two significant differences between natural lighting and artificial sources. One is the character of the fill and the other is a more rapid fall-off in intensity. In nature, skylight fill is omni-directional and usually brighter from above. That "wrap around" characteristic is difficult to duplicate with a directional artificial source.