Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm. Longer wavelengths than this are called infrared, or below red and cannot be seen by human eyes.
In human color psychology, red is associated with energy and blood, and emotions that stir the blood, including anger, passion, and love.
Red is used as one of the additive primary colors of light, complementary to cyan, in RGB color systems. Red is also one of the subtractive primary colors of RYB color space but not CMYK color space.
One common use of red as an additive primary color is in the RGB color model. Because "red" is not by itself standardized, color mixtures based on red are not exact specifications of color either. In order to produce exact colors the color red needs to be defined in terms of an absolute color space such as sRGB. As used in computer monitors and television screens, red is very variable, but some systems may apply color correction (so that a standardized "red" is produced that is not in fact full intensity of only the red colorant).