Answer:
Highlights are shades that are lighter than the allover hair color. A few of your hair strands especially in the front are highlighted. They add depth to the look of your hair.
Lowlights on the other hand are shades that are darker than the allover hair color. They are added to light color hair as they soften the look of your hair color.
Sometimes highlights and lowlights are combined to overcome the stripy look. To create real magic, you need to find a good stylist that understands your needs.