Publicly nude means nude in any place where a person may be observed by another person. Any person is nude if the person has failed to cover the rectal area, pubic area or genitals. A female person is also nude if she has failed to cover both breasts below a point immediately above the top of the areola. Each such covering must be fully opaque. No person under the age of 10 years shall be considered publicly nude.
36 CFR § 261.2
The following definitions apply to this part: