Eugenics

is defined as

"the study of or belief in the possibility of improving the qualities of the human species or a human population, especially by such means as discouraging reproduction by persons having genetic defects or presumed to have inheritable undesirable traits (negative eugenics) or encouraging reproduction by persons presumed to have inheritable desirable traits (positive eugenics)"

Source: Dictionary.com

In Startrek, The Borg are a race of cybernetic creatures. They are the arch-nemesis in Startrek and the bane of all other races in the galaxy.