Each review can have up to all four of these on it's review, to show it's a whole family read, or better suited to specific ages. Reviews with only the "Adult" stamp will of course be only suitable for adults. Junior covers all ages below 13. 13+ covers ages up to 16, or mature Juniors. YA covers ages 16 to 21, or older people that are young at heart. :) Adult are (obviously!) for adults. Hope this makes it quicker to see what age range the book will suit!