Bi-cameral parliament

A bicameral legislature is one in which the legislators are divided into two separate assemblies, chambers or houses. Bicameralism is distinguished from unicameralism, in which all of the members deliberate and vote as a single group, and from some legislatures which have three or more separate assemblies, chambers or houses. As of 2015, somewhat less than half of the world's national legislatures are bicameral.

Often, the members of the two chambers are elected or selected using different methods, which vary from country to country. This can often lead to the two chambers having very different compositions of members. Enactment of primary legislation often requires a concurrent majority, the approval of a majority of members in each of the chambers of the legislature, when this is the case, the legislature may be called an example of perfect bicameralism. However, in many Westminster system parliaments, the house to which the executive is responsible can overrule the other house and may be regarded as an example of imperfect bicameralism. Some legislatures lie in between these two positions, with one house only able to overrule the other under certain circumstances.

Although the ideas on which bicameralism are based can be traced back to the theories developed in ancient Sumer, ancient India and later ancient Greece, and Rome, recognizable bicameral institutions first arose in Medieval Europe where it was associated with separate representation of different estates of the realm. For example, one house would represent the aristocracy, and the other would represent the commoners as was the case in the Kingdom of England. Others, such as France under the Ancien Régime had a tricameral legislature known as the Estates General, which consisted of separate chambers for the clergymen, the nobility and the commoners.

...
Wikipedia