If a country has laws against miscegenation, that means they have laws against people of different races having children. If a Chinese person and an Ecuadorian person have a child, that would be considered miscegenation.
Miscegenation combines the Latin miscere, meaning “mix,” with genu, meaning “race,” plus the suffix -ation, which describes an action or process. So miscegenation means "a mixing of racial groups," like when people of different races live together or have kids together. If you read about the history of the American Civil War, you'll surely come across this word, which only came into English around that time. It's associated with offensive racist ideas of racial purity, so be careful using it.
