Eugenics is the selective breeding of a population, so as to improve the genes of said population. Eugenics has been practiced on numerous food plants for thousands of years, leading to vast improvements in said food plants. However, when people use the term 'eugenics', they are usually specificly referring to human eugenics, which is politically controversial.
Some people intend to participate in eugenic breeding, whereas others do not. See: the eugenic threshold
There are different ways in which eugenic breeding is implemented. Those are: private voluntary eugenics, and enforced eugenics.
There are different methods of eugenics. There is non-technological eugenics, which consists only of selective breeding, and there is technology-assisted eugenics, which utilizes embryo screening.