Half Head Colour What Does It Mean Half Head Of Highlights Or Full?

Half head of highlights or full? - half head colour what does it mean

At first I thought the head is full, because I do not understand what meant.Now know, I think, but if you do not allow half a head of highlights, the back of the head, completely naked in frount hard time with color?
I know that the media is cheaper, but do you think is better?
My hair is dark brown-med, and I never had, or will it be detected from its virgin hair!
Thank you for your help