Toners come in many different forms. Tinted shampoos, demi-permanent colours, foams, and sprays can all be considered as toners because they work to adjust the tone in your hair.
Purple and blue toners, like the purple shampoos and conditioners you can get from most stores, are all about eliminating brassiness. Blue toners work best for brunettes and red-heads, because the blue cancels out any sneaky orange tones. Purple toners work best for blondes, keeping your highlights looking salon fresh by reducing yellow hues.