A parliament is a body of the government, which represent the electorate (the people who can vote), make laws and oversee the government. Parliaments are an important body in democracies, for they form the base of representation of the electorate by lawmaking. The parliament is called the legislative by Montesquieu; de body who makes and approves laws.
Nearly every country has parliament and there mostly chosen in elections for a certain period. Who can and can't is different in each country. Mostly, only people with the nationality of that country and who have a certain age can vote. A parliament has one or two houses, which is also various per country. For example, Germany has one house (unicameralism) while France has two houses (bicameralism). In the case of two houses, both houses have to approve a law. These houses are called the lower house and the upper house (or senate).
Countries can have several parliaments. In Germany each federal state has his own parliament and in the United Kingdom all constitutional countries have their own parliament. In other countries, which are divided into provinces, districts or municipalities, have other names for these bodies. How much the legislative has varies per country and is written in the constitution.