A vertebra was an individual bone found in species with a spine; multiple vertebrae combined to make the spine and protect the spinal cord. The breaking of one or more vertebrae could often result in permanent injury or death.
In 2368, Worf was temporarily paralyzed when he was struck by falling containers of chlorinide in the USS Enterprise-D's cargo bay. Seven of his vertebrae were crushed and his spinal cord was severed due to the accident. (TNG: "Ethics")
Breaking one's neck was often a loud procedure due to the noise that breaking vertebrae made. Elim Garak pointed this fact out to Quark when discussing options for Quark's requested assassination. (DS9: "Body Parts")
In an alternate timeline in 2374, B'Elanna Torres suffered a ruptured vertebra during a Krenim attack; Tom Paris was prevented from immediately repairing it by The Doctor, as there were more serious cases to deal with. (VOY: "Year of Hell")
During the Hirogen's takeover of the USS Voyager in 2374, Seven of Nine received two fractured vertebrae in a holodeck recreation of World War II. Later, another crewmember suffered a fracture of the thirteenth vertebra. (VOY: "The Killing Game", "The Killing Game, Part II")
In 2375, The Doctor examined B'Elanna Torres and found evidence of internal bleeding, fractured vertebrae, contusions, and cranial trauma caused by B'Elanna's frequent use of the holodeck with the safety protocols disabled. (VOY: "Extreme Risk")