Darwinism
Darwinism is a term for the underlying concepts in those ideas of Charles Darwin concerning evolution and natural selection. Discussions of Darwinism usually focus on evolution by natural selection, but sometimes Darwinism is taken to mean evolution more broadly, or other ideas not directly associated with the work of Darwin.

# Classical Darwinism
In the 19th century context in which Darwin's On the Origin of Species was first received, "Darwinism" came to stand for an entire range of evolutionary (and often revolutionary) philosophies about both biology and society. One of the more prominent approaches was that summed in the phrase "survival of the fittest" by the philosopher Herbert Spencer, which was later taken to be emblematic of Darwinism even though Spencer's own understanding of evolution was more Lamarckian than Darwinian, and predated the publication of Darwin's theory. What is now called "Social Darwinism" was, in its day, synonymous with "Darwinism"  the application of Darwinian principles of "struggle" to society, usually in support of anti-philanthropic political agendas. Another interpretation, one notably favoured by Darwin's half-cousin Francis Galton, was that Darwinism implied that because natural selection was apparently no longer working on "civilized" people it was possible for "inferior" strains of people (who would normally be filtered out of the gene pool) to overwhelm the "superior" strains, and voluntary corrective measures would be desirable  the foundation of eugenics.
In Darwin's day there was no rigid definition of the term "Darwinism", and it was used by opponents and proponents of Darwin's biological theory alike to mean whatever they wanted it to in a larger context. The ideas had international influence, and Ernst Haeckel developed what was known as Darwinismus in Germany, although, like Spencer Haeckel's "Darwinism" had only a rough resemblance to the theory of Charles Darwin, and was not centered around natural selection at all.
While the reaction against Darwin's ideas is nowadays often thought to have been widespread immediately, in 1886 Wallace went on a lecture tour across the United States, starting in New York and going via Boston, Washington, Kansas, Iowa and Nebraska to California, lecturing on what he called Darwinism without any problems.

# Other uses
The term Darwinism is often used in the United States by promoters of creationism, notably by leading members of the intelligent design movement   to describe evolution. In this usage, the term has connotations of atheism. For example, in Charles Hodge's book What Is Darwinism?, Hodge answers the question posed in the book's title by concluding: "It is Atheism." Creationists use the term Darwinism, often pejoratively, to imply that the theory has been held as true only by Darwin and a core group of his followers, whom they cast as dogmatic and inflexible in their belief.  Casting evolution as a doctrine or belief bolsters religiously motivated political arguments to mandate equal time for the teaching of creationism in public schools.
However, Darwinism is also used neutrally within the scientific community to distinguish modern evolutionary theories from those first proposed by Darwin, as well as by historians to differentiate it from other evolutionary theories from around the same period. For example, Darwinism may be used to refer to Darwin's proposed mechanism of natural selection, in comparison to more recent mechanisms such as genetic drift and gene flow. It may also refer specifically to the role of Charles Darwin as opposed to others in the history of evolutionary thought  particularly contrasting Darwin's results with those of earlier theories such as Lamarckism or later ones such as the modern synthesis.
A notable example of a scientist who uses the term in a positive sense is Richard Dawkins.