The Borg are a fictional pseudo-race of cybernetic organisms

Cyborg

A cyborg is a being with both biological and artificial parts. The term was coined in 1960 when Manfred Clynes and Nathan S. Kline used it in an article about the advantages of self-regulating human-machine systems in outer space. D. S...

 depicted in the Star Trek

Star Trek

Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...

 universe associated with Star Trek.

Whereas cybernetics

Cybernetics

Cybernetics is the interdisciplinary study of the structure of regulatory systems. Cybernetics is closely related to information theory, control theory and systems theory, at least in its first-order form...

 are used by other races in the science fiction world (and in recent times the real world) to repair bodily damage and birth defects, the Borg use enforced cybernetic enhancement as a means of achieving what they believe to be perfection.

Aside from being the main threat in Star Trek: First Contact

Star Trek: First Contact

Star Trek: First Contact is the eighth feature film in the Star Trek science fiction franchise, released in November 1996, by Paramount Pictures. First Contact is the first film in the franchise to feature no cast members from the original Star Trek television series of the 1960s...

, the Borg also play major roles in The Next Generation

Star Trek: The Next Generation

Star Trek: The Next Generation is an American science fiction television series created by Gene Roddenberry as part of the Star Trek franchise. Roddenberry, Rick Berman, and Michael Piller served as executive producers at different times throughout the production...

 and Voyager

Star Trek: Voyager

Star Trek: Voyager is a science fiction television series set in the Star Trek universe. Set in the 24th century from the year 2371 through 2378, the series follows the adventures of the Starfleet vessel USS Voyager, which becomes stranded in the Delta Quadrant 70,000 light-years from Earth while...

 television series, primarily as an invasion threat to the United Federation of Planets

United Federation of Planets

The United Federation of Planets, also known as "The Federation" is a fictional interplanetary federal republic depicted in the Star Trek television series and motion pictures...

 and the means of return to the Alpha Quadrant for isolated Federation starship Voyager

USS Voyager (Star Trek)

The fictional Intrepid-class starship USS Voyager is the primary setting of the science fiction television series Star Trek: Voyager. It is commanded by Captain Kathryn Janeway....

, respectively.