What term refers to the expanding cloud formed from an aging star?

The term that refers to the expanding cloud formed from an aging star is "Planetary Nebula." A planetary nebula is created during the late stages of a star's life cycle, specifically when a star, like our Sun, exhausts its nuclear fuel and expels its outer layers into space. This process reveals the hot core of the star, which emits ultraviolet radiation that ionizes the ejected material, causing it to glow and form a visually stunning nebula.

In contrast, while a "Stellar Nebula" broadly refers to any cloud of gas and dust in space where stars may form, it does not specifically denote the remnants of an aging star. "Solar Flare" pertains to a sudden eruption of energy on the Sun's surface and is unrelated to the star's lifecycle in this context. The "Red Giant" phase describes a stage in a star's evolution where it has expanded and cooled after exhausting hydrogen in its core, but it does not represent the resulting cloud of gas and dust after the star has shed its outer layers. Thus, "Planetary Nebula" specifically identifies the phenomenon of an expanding cloud from the remnants of an aging star and is the correct term in this context.