Hive mind
A hive mind, group mind, collective mind, collective consciousness, or group consciousness was the linking of multiple minds into a unified whole, sacrificing individuality in exchange for the sharing of one's experiences and memories. This was often achieved through some form of telepathy. () 

The advantage of the collective mind was that it was far less likely for the combined whole to make the same mistake a single leader could make. ()

Borg 
Perhaps the most notable example of a collective consciousness encountered by Starfleet was "the Hive", or more formally known as the Borg Collective, in which all Borg drones existed, sharing thoughts, memories, and functions. (; ; ) 

For most individuals, joining the Hive was not considered a desirable prospect. While lost in the Delta Quadrant during the 2370s, the crew of  avoided it as much as possible. ()

The Borg hive mind was controlled through a central plexus, found aboard every Borg vessel, which was, in turn, connected to a neural network that was directly controlled by the Borg Queen through the Unicomplex. (; ) These signals, which were interactive across a subspace domain similar to that of a transporter beam, where hypothesized by Data to be subspace signals on frequencies that form the basis of the Borg's collective consciousness. () Each drone was identified and communicated with through its own translink signature. () 

When the  was boarded by the Queen and a number of her drone, they established a collective in the ship's main engineering, which was used as a central point from which they could control the Hive. ()

After both Jean-Luc Picard and Seven of Nine were assimilated by the Borg, they were linked to the Hive mind, which then restructured their synaptic pathways, and purged their individuality. (; ) Once the neural pathways were restructured, the newly minted drone was linked to a single collective mind. () The neural patterns of former individuals were then integrated into the Hive mind and were, then, stored within the cortical implants found within the mind of each drone. ()

In many cases, Borg removed key circuits from injured comrades, typically those who were damaged beyond repair, to separated them from the group consciousness, after which, the injured Borg was discarded and immediately self-destructed. (; ) After a drone was deactivated, its memories up to that point continued to reside in the Borg Collective's consciousness, meaning that, as long as the hive existed, so did a part of that drone. ()

When a drone became disconnected from the Hive mind, ex-Borg generally became confused, irrational, and afraid. () The loneliness felt for these former drones was an overall terrifying experience, and often left feeling damaged, but regaining individuality was often achievable. () Doctor Beverly Crusher likened the process of removing a drone from the collective consciousness to asking an individual "to disconnect an arm or a foot". () Captain Picard stated a similar reference to Dr. Crusher, describing a Borg drone as "a single, collective being," emphasizing that "[t]here's no one Borg who is more an individual than your arm or your leg." ()

The Borg's neural interface could be used to interconnect a neural link among those disconnected from the Hive mind to establish a localized group mind. () 

For Seven of Nine, being a part of the Borg Collective established a sense of order, an order that continued to be a source of strength for her, even after being disconnected from the Hive. To her benefit, the sense of order that was taken from the Hive, was also what allowed her to regain her humanity. () When  was later tasked with locating the source of the Omega particle in 2374, Seven used her "hive mentality" to establish teams to quickly and efficiently complete the mission at hand. At that time, Harry Kim complained that her doing so was going "just a little too far," as she had "designated functions, numbered drones" to each of the crewmembers involved. ()

In an alternate 2404, the curriculum for the Starfleet Academy course on the Borg Collective taught about the assimilation process, the Borg hierarchy, and the psychology of the Borg hive mind. ()

Examples
 Androids of planet Mudd were connected through a central control complex. ()
 The Body of Landru. ()
 Changelings lived together in the Great Link. ()
 Flying parasites that infested Deneva in 2267 existed as  in an incredibly huge organism, that were guided by and drawing their strength from the whole. ()
 Medusans lived together in hive minds. ()

In addition, the Dream Aliens shared a "collective unconsciousness" in which they all inhabited a common dream. ()

See also
 Collective unconsciousness
 Collective intelligence

External links 
 
 

de:Hive-Bewusstsein
Borg
Physiology