Clothing optional
Clothing optional or CO refers to resorts and beaches that allow clothing to be worn at the option of the guest. Some people new to the nude scene appreciate the option to be clothed or not, in whatever degree of coverage they desire. Many report that after a short period of time at a CO resort they prefer total nudity anyway. Publicly accessed "Nude beaches" are actually clothing optional beaches, as there is no enforcement mechanism to make sure that all in attendance are nude at all times.
There are resorts that are nude resorts, where the requirement is full nudity when in and around the pools, private beaches or other specified areas. Some people appreciate that at a nude resort all the guests are in the same boat, all required to be completely nude. Typically, a coverup of some sort is appropriate when dining (though not required), and it is ALWAYS appropriate to carry a towel to sit on.
European nude resorts frequently allow specific exceptions for pubescent children who might prefer not to be nude. The view is that it is preferable to respect their wish for personal privacy rather than apply the rules too rigorously, since that might provoke family dissent and lead to the entire family leaving the resort. The clothed option is taken up by boys very much more than girls.