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G "General". A story with this rating is suitable for any age group and won't contain any implied violence or sex, or swearing/cussing.

PG "Parental guidance suggested". Story may contain cussing/swearing, or other topics that may not be appropriate for young children, but isn't adult either.

PG-13 "Parental guidance suggested for children under 13" Story may be unsuitable for children under the age of thirteen due to implied sex or violence.

R "Restricted". The story contains adult themes such as sex or violence, but it is not of an explicit nature. Generally speaking, they would be unsuitable for anyone under 15.

NC-17 "No children under 17" Story is unsuitable for anyone under the age of consent due to explicit sex, violence or other adult topics such as strong angst and/or suicide.