From the greatest fountain of human knowledge ever constructed: Wikipedia.
(All of science is a very close second.)
Elementary art education materials, dictionaries, and electronic search engines often define primary colors effectively as conceptual colors (generally red, yellow, and blue; or red, green, and blue) that can be used to mix “all” other colors and often go further and suggest that these conceptual colors correspond to specific hues and precise wavelengths. Such sources do not present a coherent, consistent definition of primary colors since real primaries cannot be complete.(Source)