Political policy and ideaology motivated by practicality, not ethics or morality. In realpolitik, the goal is securing or improving one's own interests, not doing the 'right thing' or helping other people.
Example in action: nearly all American foreign policy, particularly under the George W. Bush regime.
A term to describe or prescribe politics based on strictly practical rather than idealistic notions, and practiced without any sentimental illusions.
In Germany, the term Realpolitik is more often used to distinguish modest (realistic) politics from overzealeous (unrealistic) politics. That Prussia didn't demand territory from defeated Austria provided the impetus for coining this term, as was the sometimes very slow or indirect steps towards German unification under Prussia. Realistic compromises are reached instead of clinging to values like justice or nationalism.
In the United States, the policy of Realpolitik was formally introduced to the Nixon White House by Henry Kissinger. In this context, the policy meant dealing with other powerful nations in a practical manner rather than on the basis of political doctrine or ethics — for instance, Nixon's diplomacy with the People's Republic of China, despite the U.S.'s purported opposition to communism and the previous doctrine of containment. Another example is Kissinger's 'green lighting' of dictator Suharto's invasion of East Timor.
See also: the novel "Mating" by Norman Rush. There is a scene where the ambiguity of the definition, and its proper pronunciation, are used to great effect.
See above example--literary.