Realism, or painting one's surroundings as accurately as possible, developed in France in the mid 1800's. They argued that only the things of one's own time is reality. They concentrated their subject matter on everyday experiences, and aspects of their current life and shunned anything that could not be seen or experienced. They dared to paint the poor, the mundane, devoting their skills that in previous eras would be devoted to historical paintings.

In Jean-Francois Millet's The Gleaners you see a group of women bent over picking up the remains of the harvest, so desperate for food that they pick the leftovers off the ground in order to survive. That was a reality of their time, and Millet painted it.

Realism is not without controversy. In Edouard Manet's Olympia, a prostitute sits lying nude engaging the audience. She wears nothing except a black ribbon tied around her neck and high-heeled shoes. While the people of his time were used to nudes, they weren't used to the nudes looking out into the audience unashamed or unembarassed by their nudity. People of the time found it quite shocking and morally depraved.
Source: Gardener's Art Through The Ages
