Pretty much what it sounds like.
Climate change deniers reject atmospheric science "
Most creationists reject the science of evolution
Apollo hoaxers reject the science
People often believe things very strongly, and when science is in conflict with their beliefs, they go with their beliefs.
Including, of course:
Those who reject blindly certain obvious possibilities of human evolution, such as the "wading ape" hypothesis;
those who reject blindly certain long obvious possibilities of anthropological discovery, such as densely populated and sophisticated civilizations widespread in the Americas;
those who reject blindly certain obvious possibilities of sociological and biomedical discovery, such as the influence of racial bigotry on a wide variety of phenomena;
Those who reject blindly certain aspects of economic reality, including consistently irrational agent behavior and suboptimal equilibria in market economies;
those who reject sound criticism of current GMO research and deployments, including corporate influences and major risks of the technology both known and unknown;
and so forth.
Many of these blanket denials and rejections of what are in all other respects perfectly sound "scientific" arguments, established possibilities, even straight ahead observations, are by established scientific researchers and organizations and academics of high repute. Many feature startlingly obtuse, inadequate, and unsound "arguments" notably similar to those of creationists and CO2 deniers.
Calling it "science denial", while accurate, can obscure its agency in some areas.
