A dictionary defines race as "a division of mankind possessing traits that are transmissible by descent and sufficient to characterize it as a distinct human type" but in practice, 'races' tend to be characterized more by their position of power or powerlessness in a society than by any innate traits. Biologically, no transmissible (genetic) traits are sufficient to characterize a person as belonging to one race or another. Scientists classified the population of the world into different races hundreds of years ago based on observed characteristics, but it is now generally agreed upon that race is a social construct -- a fiction which persists for complex reasons we will try to explore here. Racism is commonly understood to be prejudicial discrimination based on race -- i.e. the notion that you can gain some information about someone's intelligence, values, personality, etc. by observing the color of their skin. It follows from this notion that certain races are inherently better than others. Many find that a more useful definition encompasses the issues of power and oppression that are involved in racial discrimination. Defining racism as "racial prejudice plus power" means that when one group of people uses the notion of racial distinctions to deny power to others, this group of people can be considered racist. According to this definition, when an individual behaves in a prejudicial manner that behavior is considered racist only if it accords that person's racial group power. The power gained by subjugating a large population based on some easily observed physical characteristics is one of the many reasons racism continues to be difficult to eradicate.