A parliament is a body of usually elected representatives that forms part of the government of a country, or of part of a country. The exact role of a parliament depends on the constitution of the place it governs, but most parliaments are charged with making and amending laws, and may have to ratify government spending and hold ministers to account.
It is common for parliaments to have more than one chamber, for example the United Kingdom has the House of Commons and the House of Lords, and the United States of America's federal government has the Senate and the House of Representatives. Usually, one chamber handles day-to-day matters while the other has a longer term role and acts as a check on the activities of the first.
In many countries, the head of government is chosen from among the representatives that make up the most important chamber of parliament; this role is often called the Prime Minister. The Prime Minister is often the most powerful person in the government (eg in the United Kingdom, Spain and Australia), although this varies from one country to another. In particular, republics often confer more power on the president's role; this applies to the United States, which does not use the title Prime Minister, and France.