Regeneration was a process of repair or renewal. Regenerating damaged tissue was an important field in medicine. In addition, regeneration was a natural activity undertaken by some species during their resting cycle, analogous to sleep.
Medical usage[]
In 2377, The Doctor found a way to adapt Borg regeneration techniques to treat Dr. Lewis Zimmerman's acute subcellular degradation. (VOY: "Life Line")
Natural usage[]
The nucleogenic cloud being encountered by the USS Voyager in 2371 in the Delta Quadrant had the ability to regenerate. To assist this regeneration process, Voyager transfered a nucleonic beam into the lifeform. (VOY: "The Cloud")
Borg[]
Borg drones regenerated in Borg alcoves. These alcoves were found aboard Borg vessels and also aboard the Voyager, where Seven of Nine and later the Borg children regenerated. (VOY: "The Haunting of Deck Twelve"; Star Trek: First Contact)
A Borg drone can function for up to 200 hours before needing to regenerate. Seven of Nine, once she was separated from the Collective, needed to regenerate for at least three hours a day to maintain her health. (VOY: "Hunters")
Borg drones also regenerate outside of their alcoves when nanoprobes repair the drone itself, with their cybernetic components being undergoing maintenance and repair on a microscopic level, as they could also repair cells. (ENT: "Regeneration")
When Seven of Nine discussed Icheb's regenerative needs to Leucon, she explained how she had adapted a neural transceiver to interface with a portable regenerator. Seven figured the device had enough power to complete one full cycle for Icheb; before adding that "[i]t's important that Icheb regenerate for six uninterrupted hours." It can be presumed she provided Azan, Rebi and Mezoti with such devices when they left Voyager. (VOY: "Child's Play", "Imperfection")
Borg drones could also regenerate and repair damage to a Borg ship, such as a Borg cube or a Borg sphere from the alcoves. (TNG: "Q Who"; VOY: "Dark Frontier")
The effect of the Borg cube's regeneration in "Q Who" was created by building a scale replica of a Borg cube's 'wall', melting it with a blowtorch, and then playing the footage in reverse during filming. (citation needed • edit)
Sometimes, disturbing thoughts could interrupt a Borg's regeneration cycle. (VOY: "Child's Play")
Changelings[]
A Changeling could only remain in solid form for sixteen to eighteen uninterrupted hours, at which time they needed to revert to a gelatinous state. (DS9: "The Storyteller", "The Forsaken", "The Alternate", "The Search, Part I"; DS9: "A Man Alone", "In Purgatory's Shadow")
Failure to do this could lead to damage to their morphogenic matrix, which manifested as discoloration and "flaking off" of mass. (DS9: "The Die is Cast")
Jadzia Dax often entered Odo's quarters while he was regenerating and moved several pieces of his furniture, only by a few centimeters, knowing this would irk the constable. (DS9: "Homefront")
After Odo (serving as umpire) called a strike in a baseball game between the Niners and the Logicians, Benjamin Sisko claimed that Odo must have been regenerating and not watching the game at all. (DS9: "Take Me Out to the Holosuite")
Gideons[]
Gideons were continuously regenerating their bodies, which meant that, save for accident and disease, they were immortal. (TOS: "The Mark of Gideon")
Species 8472[]
In 2373, Lieutenant Tuvok detected that damage to a wall inside a Species 8472 bio-ship was caused by a Borg disruptor beam. However, the wall appeared to be regenerating itself. (VOY: "Scorpion")