Political science is the study of
governance. Governance is a slightly more encompassing concept than
government: it refers to how decisions are made in groups, and what kinds of structures are created to organize societies. In the
international arena, for instance, there is no fixed government, but there
are bodies that govern (e.g. the
United Nations).
For most purposes, political science can be broken down into two halves: government and international relations. Many universities treat the two as separate curricula, but the tradition has been to integrate the two on the undergraduate level, as the concepts of one rely heavily upon the concepts of the other. Public policy, public administration, and security studies are also sometimes treated as separate disciplines, especially for graduate studies where many students are looking for career-building material. In fact, the only people you're likely to find studying vanilla "political science" after receiving their bachelor's degree are those political junkies destined to become professors and talking heads. It may not be a bad idea, since the average Ph.D. in political science earns nearly $80,000 a year after graduation.
As a poli sci major, I often get the question: "What do you do with a degree like that?!" Well, since it's a liberal arts degree, the correct answer is "Anything you damn well please." Most people who study poli sci, however, are either looking into law school, the foreign service, or the world of Washington insidership and lobbying. Some disappear into the Central Intelligence Agency or the Pentagon, never to be heard from again. More than a few get their teaching certification and enter the wild world that is education.
Still, most poli sci majors are looking for a career track that will take them to the upper echelons of the American bureaucracy, and perhaps even elected office. This means that a great many of them seem to be clones of Reese Witherspoon's character from Election, the power tripping and often hideously preppy opposites of students in engineering or fine arts. They are the lawyers and Henry Kissingers of the future, so this is hardly surprising. However, there are a few political science majors out there who manage to avoid being sucked into the evil image of entities like the State Department. They just take some time to uncover.
The best poli sci programs in the United States are at the Ivy League schools (Harvard's John F. Kennedy School of Government is consistently ranked #1), Georgetown University, and Stanford University. Many schools treat poli sci as a quantitative science, stressing the statistics side over the philosophy side; some even offer BS programs in the field.