What is political ideology?
A political ideology is a set of political beliefs. In other words, an ideology is a collection of ideas, usually revolving around a central assumption or belief, that people think should govern society.
Usually we compare political ideologies by putting them on a spectrum, with the left being in American politics more liberal, and the right more conservative. To give examples in an American context, "liberalism," the more left-leaning ideology in American politics, argues among other things that society ought to do more to foster equality and social justice among people. In many cases, this entails government action, as in the New Deal of the 1930s, or the Great Society of the 1960s, touchstones for modern liberalism. "Conservatism," the more right-leaning of the ideologies in American politics, argues, among other things, for more emphasis on economic freedom than on equality or justice. Typically conservatives position themselves against government regulation and attempts to create social justice and equality, arguing that they often result in unintended consequences and involve enormous expense.
These are only two relatively moderate examples of political ideology, and it should be noted that "Republican" and "Democrat" are political parties, not ideologies. Parties are aligned to particular ideologies (more at some times than at others) but are not synonymous with them.