"Clad only in the sky". Ritual nakedness. Some include not wearing jewellery, hair adornments and makeup as being skyclad. Many people believe that when you perform rituals naked you are free from restrictions and falsehood. Some say magick is more powerful when performed in this way.
Skyclad is a British heavy metal band with heavy folk influences in their music. They are considered one of the inventors of folk metal, the other major influence on the genre being Bathory. For the meaning of the name, see Skyclad.