Government refers to the structure of institutions that make collective decisions for a society. Types of government vary by distribution of political power, but in general, most forms fit into one of three categories.
The three main types of government are
Under a monarchy, meaning rule of one, all governmental power is traditionally vested in a single ruler, usually a king or queen. However, in some modern monarchies, such as the United Kingdom, the monarch’s function is largely ceremonial.
The term comes from Greek, meaning “rule by many.” In a democracy, the people themselves exercise political power directly, or through elected representatives.
The governments of the United States, and many Western nations are basically democratic, although their characteristics vary.
India, with a population over more than 1 billion, is often referred to as the world’s largest democracy.
Oligarchy means rule by the few, in which a small elite controls political power. Oligarchic systems range from military dictatorships to one-party totalitarian systems, such as those in China, North Korea, and the former Soviet Union.
Source: Three Types of Government | eHow.com