Right-wing
In politics, right-wing, the political right or simply the right, are terms that refer to the segment of the political spectrum often associated with any of several strains of conservatism, the religious right, and areas of classical liberalism, or simply the opposite of left-wing politics.
The term originates from the French Revolution, when liberal deputies from the Third Estate generally sat to the left of the president's chair, a habit which began in the Estates General of 1789. The nobility, members of the Second Estate, generally sat to the right. In the successive legislative assemblies, monarchists who supported the Ancien Régime were commonly referred to as rightists because they sat on the right side. It is still the tradition in the French Assemblée Nationale for the representatives to be seated left-to-right (relative to the Assemblée president) according to their political alignment.
http://en.wikipedia.org/wiki/Right-wing_politics
Left-wing
In politics, left-wing, the political left or simply the left are terms that refer to the segment of the political spectrum typically associated with any of several strains of, to varying extents, socialism, anarchism, communism, social democracy, liberalism or social liberalism, and defined in contradistinction to its polar opposite, the right.
http://en.wikipedia.org/wiki/Left-wing_politics
Centrism
In politics, centrism usually refers to the political ideal of promoting moderate policies which land in the middle ground between different political extremes. Most commonly, this is visualized as part of the one-dimensional political spectrum of Left-Right politics, with centrism landing in the middle between left-wing politics and right-wing politics. However, there is arguably more than one dimension to politics, so even the centre has its own radicals as exemplified by radical centrist politics.
http://en.wikipedia.org/wiki/Centrism