黄矮星，在天文学上的正式名称为GV恒星，是光谱型态为G，发光度为V的主序星。这一类恒星的质量大约在0.8至1.0太阳质量，表面的有效温度在5,300至6,000K。与其他的主序星一样，GV恒星在核心进行将氢融合成氦的核融合反应。太阳是最著名的，也是最易见到的GV恒星（黄矮星），每秒钟将大约6亿吨的氢转换成氦，将400万吨的质量转换成能量。 其他的GV恒星，还有南门二（半人马座α）、鲸鱼座τ和飞马座51。

黄矮星其实是一个错误的名称，因为光谱类型为G的恒星实际颜色是从白色到黄色的，像太阳在早期的颜色是白色，只有到晚期才会成为黄色。 参考光谱分类的颜色与光谱图，太阳实际上是白色的，被错误的看成黄色是因为背景的蓝天造成的（在蓝色的衬托下变得偏黄），而在地平线附近的太阳呈现红色，则是大气层的瑞利散射造成的。

A G-type main-sequence star (Spectral type: G-V), often (and imprecisely) called a yellow dwarf, or G dwarf star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K. Like other main-sequence stars, a G-type main-sequence star is in the process of converting the element hydrogen to helium in its core by means of nuclear fusion. The Sun, the star to which the Earth is gravitationally bound in the Solar System and the object with the largest Apparent magnitude, is an example of a G-type main-sequence star. Each second, the sun fuses approximately 600 million tons of hydrogen to helium, converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.