From the Greek for "Well Born"
What is eugenics? Literally, the term means “well-born," from the Greek eu (well or good) and gene (born). The broader meaning of what was encompassed by the concept of eugenics however, was harder to pin down for Galton, and has been confusing throughout the entire history of eugenics thought, even to this day. Indeed, Galton defined it in many ways, including “the study of all agencies under human control which can improve or impair the racial quality of future generations", as well as “the science which deals with all influences that improve the inborn qualities of a race; also with those that develop them to the utmost advantage."
Very generally, eugenics became related to influencing differential birth rates in order to create a human society characterized by an over-abundance of “desirable" traits and a decrease in, or a complete elimination of, “undesirable" traits. In the late 19th and early 20th centuries, the idea of bettering society through science was so widespread that virtually every country around the world had some kind of eugenics policy in place. The countries differed, though, in whether they practiced positive or negative eugenics. The difference between the two is that positive eugenics focuses on increasing the presence of desirable traits, while negative eugenics focuses on decreasing the presence of undesirable traits.
Countries focused on negative eugenics, as well as coercive practices, and using eugenics to further strong racial and/or class prejudices, caused the most damage to the movement by engaging in such practices as segregation, sterilization (often involuntary), and, in the case of Germany's Third Reich, genocide. Most countries, however, focused their eugenic campaigns on making birth control widely available, rewarding “undesirables" for not having children or for voluntary sterilization.