Nude is not wearing anything to cover ones skin. Everyone gets nude from time to time to take a bath or shower.
Nude is not the same as naked. Naked is stripping off ones clothing for the enjoyment of others. Many people get naked to have sex.
Nude is definitely not the same as nekkid. Nekkid is stripping off ones clothing and running around, not just for the enjoyment of others, but oneself, too.
Whilst there are nudists who get naked or even nekkid, there are not nakedists nor nekkidists. The latter groups are called exhibitionists.
Fine art models are nudes, not nudists. Although, a nudist can be a nude model. It is difficult to get a nekkid gal to be a fine arts nude - she wants to run around too much.
At some few places it is prohibited to be nude