Someone who's nude isn't wearing any clothes. In modern society, we're generally nude in the shower but fully dressed when we go to work.
Whether you say you're "in your birthday suit," "au naturel," or "unclothed" — when you're nude, you're naked. You might find the word in the phrase "in the nude," which also simply means nude, or describing a work of art as "a nude," or a painting or sculpture of a nude person. In the 1500s, nude was a legal term meaning "unsupported," from the Latin nudus, "bare." The "naked" definition didn't became popular until the nineteenth century.