Regeneration is an activity undertaken by some species during their resting cycle, analogous to sleep.
Borg
Borg regenerate in Borg alcoves. Borg alcoves were used on USS Voyager to allow Seven of Nine to regenerate. Later, they were also used by the Borg children and adolescents that joined the crew. (VOY: "The Haunting of Deck Twelve")
Changelings
A Changeling can only remain in solid form for sixteen uninterrupted hours, at which time they must revert to a "gelatinous" state. (DS9: "The Forsaken")
Failure to do this can lead to damage to their morphogenic matrix which manifests 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")
See also
- Cellular regeneration and entertainment chamber
- Vascular regeneration