Realism as a movement began in painting circles as a reaction to the romantic movement. In painting, this means to represent an object exactly as it appears in life. This school of painting hit France in the 19th Century. Romanticism is a much more highly subjective approach to art which is very intense, emotional or dreamlike.
The movement moved from art to literature with authors such as Balzac and Flaubert from France. From France to England with Writer George Eliot "giving a faithful representation to commonplace things" in her novel, Adam Bede.
From England to America through the writings of Henry James, William Dean Howells, and Mark Twain, the idea of a person simply being a perons catches on. Realist writiers attempt to set down the common-place occurrences in life objectively without writing around pre-conceived notions or ideals. These novels are fairly true-to-life accounts which focus on middle-class life.
The best example of realism in American Liture that I can think of is The Jungle by Upton Sinclair. This novel was written late in the realist period and described the life of a factory worker in turn-of-the-century Chicago.
The realist movement started in France in the 19th Century and took as its primary aim the desire to narrate a story from a objective perspective that simply and without unnecessarily ornation presented the facts of the story. It most fully finds its expression in the novel form, and some realist novels have become known as some of the best examples of novels in literature. Realist writers became known for accurate psychological representations of characters and their ability to present every day life settings with accuracy and an eye for detail. Realism was distinct from previous movements of literature in its desire to present people from all walks of life (both rich and poor) and this is why many realist novels explore the differences between rich and poor sectors of society.
Although the movement started in France, it spread quickly, and in the English canon famous authors who can be considered to be realists are Dickens and Eliot. Dickens in particular is reponsible for bring to light the reality of life for the urban poor in London.