This page contains information regarding Star Trek: Lower Decks, and thus may contain spoilers.
"Oh, come now! A big, handsome, strapping fellow like you? What can you be afraid of?"
Nudity refers to the state of not wearing any clothes. Most sentient species remove their garments to become naked when they have sexual relations. Some cultures - such as Humans and Vulcans - considered nudity to be somewhat risqué and titillating. (citation needed • edit) However, other cultures - such as the Edo - considered nudity a normal part of everyday life, however. (TNG: "Justice")
On the planet Exo III in 2266, the android Ruk locked Captain James T. Kirk nude onto an android duplicator to aid Dr. Roger Korby, the long-lost fiancé of Nurse Christine Chapel, to create an android duplicate of Kirk in order to take over the USS Enterprise. The purpose of this ploy was to further Korby's plan to populate the universe with other androids. (TOS: "What Are Little Girls Made Of?")
Individuals attending Betazoid wedding ceremonies were traditionally required to be completely nude, including the participants and the guests. In 2368, Lwaxana Troi arrived to her wedding to Campio aboard the USS Enterprise-D in the nude, over the protests of Campio's Protocol Master, Erko. (TNG: "Haven", "Cost of Living"; Star Trek Nemesis)
Data, a Soong-type android, had no concern with nudity when he was first activated, as his programming led him to see no practical necessity to wearing clothing as he did not suffer from the elements. This led his creator, Dr. Noonian Soong, to add a modesty subroutine to his programming. (TNG: "Inheritance") In 2366, when Data was kidnapped by Kivas Fajo, he refused Fajo's demand that he wear a specific set of clothes instead of his Starfleet uniform. Fajo destroyed the uniform with finoplak, triggering Data's modesty subroutine and forcing him to change into the clothes. (TNG: "The Most Toys")
A line in Henry V stated, "For though I speak it to you, I think the king is but a man, as I am. The violet smells to him as it doth to me, in his nakedness he appears but a man." (TNG: "The Defector")
Nudes were often the subject of artistic representations. In 2366, Captain Jean-Luc Picard, Ensign Williams, and Lieutenant Wright attended an art class on the Enterprise-D wherein each painted a canvas of a nude model. (TNG: "A Matter of Perspective")
In 2369, Jean-Luc Picard was stripped of his clothes by the Cardassian Gul Madred as part of his torture and interrogation. Miles O'Brien also suffered a similar situation when he was arrested by the Cardassians. (TNG: "Chain of Command, Part II"; DS9: "Tribunal")
On Deep Space 9, in the weeks leading up to the Dominion War, Morn went berserk after hearing Quark's prediction of the coming doom. He hit Quark with a barstool, and ran out of Quark's and through the Promenade, screaming "We're all doomed!" He then ran into the Bajoran shrine, stark naked, and began crying to the Prophets for protection. (DS9: "Blaze of Glory")
One of the more risqué fantasies of The Doctor involved painting Seven of Nine in the nude. When Captain Kathryn Janeway observed his fantasies in 2376 on the holodeck as part of an attempt to fix an error in his programming, she commented that he drew the holographic Seven's hands very well. Later, after the problem was resolved, the real Seven gave him a kiss, but told him that it was a platonic gesture, and that he should not expect her to pose for him. (VOY: "Tinker Tenor Doctor Spy")
One of Ensign Beckett Mariner's favorite holodeck programs was an all-nude Olympic Training room, which she showed to Ensign D'Vana Tendi after introducing her to the holodeck on the USS Cerritos in 2380. Upon seeing the program, Tendi said that it was "very detailed". (LD: "Second Contact")
The Star Trek: The Original Series episode "Patterns of Force" marks the only time, in any Star Trek series or film, that Spock actor Leonard Nimoy is seen on camera without a shirt. (Star Trek: The Original Series 365) William Shatner, however, appeared shirtless twelve times, and in a ripped shirt seven times. 
According to the Star Trek: The Next Generation Companion (2nd ed., p. 74), in the episode "Unnatural Selection", "the Darwin 'superchildren' were originally to have appeared nude and the extras were asked to shave from the neck down. But the use of transparent furniture quickly nixed that idea, and costumes were hastily made as the extras endured stubble itch."
The Parallax colony's mud bath that Lwaxana Troi, Alexander Rozhenko, Deanna Troi, and Worf use in "Cost of Living" is implied to be done in the nude. The episode also ends with the second bare female bottom, namely Lwaxana's, to appear in Star Trek, after the art model in "A Matter of Perspective".
The scene in the Star Trek: Deep Space Nine episode "Let He Who Is Without Sin..." in which Worf walks in on Leeta and her Risian companion in a purple mesh tank top, Leeta was originally naked and in a bath tub. This is evident in the original thirty-second promotional spot, available at startrek.com. Chase Masterson commented: "Sometimes fans ask why there was a different scenario, including wardrobe, shown in the massage scene previews of "Let He Who Is Without Sin" than when the episode aired. We originally shot the scene on a closed set, with very little clothing. Then – and I'll never forget this day – I got called into Rick's office, and he told me, "We have to reshoot the massage scene because it's too sexy for Star Trek." I said, "Wow, thank you! I mean – I'm sorry!" I’m really glad we redid the scene – it's much more elegantly done than the original." 
The butterfly dancers in Star Trek: Enterprise's premiere episode, "Broken Bow", wore little more than seven layers of foul-smelling latex, which took nine hours to be painted. Diane Klimaszewski, who played the blue butterfly dancer, passed out and vomited due to the appliances. Despite these physical reactions to the latex, she considered the episode worth the discomfort. Regarding the experience of creating the scene in which she and twin sister Elaine Klimaszewski played the pair of aliens, Diane recalled, "We each had our own trailer and we were filming by the beach, near a water treatment plant. I had my trailer door open, so passers-by would look in and freak out to see this alien!" (Star Trek Magazine issue 119, p. 43)
As originally filmed, the famous "love scene" between Trip Tucker and T'Pol in the Star Trek: Enterprise episode "Harbinger" featured a look at actress Jolene Blalock's naked posterior. Two versions of this scene exist, however, depending on where and how the episode is watched; US audiences watching the original broadcast on UPN, or later on the Sci-Fi Channel, were shown a version in which the frame was "enlarged," enabling the network to crop the picture just above Blalock's bare bottom. Canadian viewers, however, were treated to the scene as it was originally shot – with Blalock's bottom shown (see the picture to the left). The "unedited" version of this scene is intact on the DVD release of the episode, HDNet's broadcast, and streaming video providers such as Netflix and Hulu. The episode aired ten days after the "wardrobe malfunction" during halftime at Super Bowl XXXVIII, which may have resulted in the alternate versions. This is the third time a bare female bottom was in Star Trek, though it was the first time more than one "cheek" was shown.
The Star Trek: Discovery episode "Into the Forest I Go" was the first Star Trek episode or film to show female frontal nudity on-screen, albeit briefly, in the form of the Klingon L'Rell's nipples in Ash Tyler's flashback/nightmare.