How do you describe a quarter moon?

A quarter moon, also known as a first or last quarter moon depending on its phase, appears as a half-lit circle in the night sky. This occurs when the Moon is at a 90-degree angle relative to the Earth and Sun, resulting in half of its surface being illuminated and the other half in shadow. The illuminated portion can be seen as a bright, curved line separating the light and dark sides. This phase is often characterized by its distinct shape and is a popular sight for stargazers.