What is the term used for the boundary between daylight and darkness on the Moon?

The boundary between daylight and darkness on the Moon is referred to as the terminator. This term describes the shifting line where the illuminated part of the Moon meets the dark, unlit portion. The terminator is significant because it is where sunlight creates sharp contrasts between light and shadow, making it an area of particular interest for lunar observation. The appearance of features like craters and mountains is enhanced due to the angle of sunlight at this boundary, allowing for a better understanding of the lunar terrain.

While other terms might describe boundaries or transitions in different contexts, none specifically refer to the lunar daylight-darkness line like the term "terminator" does. The horizon represents an observer's visible boundary between the land and sky, the shadow line could imply a more generalized boundary without the specific lunar context, and the twilight zone is typically used to describe the transition areas on Earth, not specifically on the Moon. Therefore, the use of "terminator" is accurate and essential within the context of lunar geography.