Unobtainium is a fictional material often used in science fiction to describe a substance that is extremely rare, valuable, or difficult to obtain. The term is commonly employed to highlight the challenges of acquiring certain resources or technologies in various narratives, including movies and literature. In engineering and design, unobtainium can refer to an idealized material with perfect properties, such as being lightweight, strong, and resistant to heat. This concept helps illustrate the limitations of current materials and inspires innovation in creating new substances that could meet these high standards.