1.
fixed star, star (astronomical)
A celestial body that generates its own light through nuclear fusion, as opposed to planets which reflect light. The sun is the nearest star to Earth.
Similar words
恒星 (star) vs. 惑星 (planet): Stars emit their own light; planets orbit stars and reflect light. In everyday Japanese, 星 covers both stars and planets in casual speech, while 恒星 is the precise scientific term.
Etymology
The characters 恒 (constant, permanent) + 星 (star) reflect the historical observation that stars appear fixed in position relative to planets, which visibly move across the sky.