Magenta is a color made up of red and blue light. A common precise definition for the color does not exist--however, in printing, the color is made up of equal parts of red and blue. As such, this shade magenta is the complement of green: magenta pigments absorb green light. In any case, it is not a spectral color: it cannot be generated by light of a single wavelength.
Along with yellow and cyan, a magenta made up of equal amounts of red and blue constitutes the three subtractive primary colors.
Magenta, properly speaking, is a variant of purple. A specific shade of magenta, fuchsia, was assigned as an alias for the RGB code of magenta on a list of standardized web colors. In general use, magenta itself can vary from the deep pink color shown below to the purple shade shown above. This specific variant of magenta is also called Fuchsia after the color of the flowers of the same name, named after Leonhart Fuchs.
If the visible spectrum is wrapped to form a color wheel, magenta appears between red and blue:
Magenta (kleur) | Magenta | Magenta (Farbe) | Magenta | Magenta (couleur) | Maxenta | Magenta (colore) | מג'נטה | Magenta (kleur) | マゼンタ | Magenta | Magenta (barwa) | Magenta | Маджента | Magenta | Magenta | Galibarda | 品紅色