特超巨星（Hypergiant）在约克光谱分类中的光度属于0（是数字的零，不是字母O），位置在赫罗图的最上方，是一种具有极高质量与光度的恒星，显示它们质量流失非常大。

即使有更精确的定义，特超巨星通常是指一种结构最为松散的大质量恒星。在1956年，天文学家Feast和Thackeray使用超超巨星（super-supergiant）这个名词（之后才改为特超巨星）来描述绝对星等高于M_V =-7的恒星。在1971年，肯那建议这个名词只应使用在有着明显的H-α发射谱线的超巨星，表示这是有着扩张的恒星大气层或相对而言有高速率质量流失的恒星。肯那的这个准则在今天仍是科学家最常用的，这意味着特超巨星的质量无须比相似的超巨星更大。现在，大部份的大质量恒星都被认为是特超巨星，质量的范围在100-150太阳质量。

A hypergiant (luminosity class 0 or Ia) is a star with an enormous luminosity showing signs of a very high rate of mass loss.

The word hypergiant is commonly used as a loose term for the most luminous stars found, even though there are more precise definitions. In 1956, the astronomers Feast and Thackeray used the term super-supergiant (later changed into hypergiant) for stars with an absolute magnitude brighter than M_V = −7 (M_Bol will be larger for very cool and very hot stars, for example at least −9.7 for a B0 hypergiant). In 1971, Keenan suggested that the term would be used only for supergiants showing at least one broad emission component in Hα, indicating an extended stellar atmosphere or a relatively large mass loss rate. The Keenan criterion is the one most commonly used by scientists today. Additionally, hypergiants are expected to have characteristic broadening and red-shifting of their spectral lines producing a distinctive shape known as a P Cygni profile. The use of hydrogen emission is not helpful for defining the coolest hypergiants, and these are largely classified on luminosity since mass loss is almost inevitable for the class.