A bicameral system, also known as bicameralism, is a system of government in which the legislature comprises two houses.
Originally, the "upper house" were often chosen from the wealthy and/or the nobility/clergy, often argued to be wiser persons. Influenced by the Senate of Ancient Rome, the Senate of the United States was originally not elected, but instead wealthy and argued wise persons, selected by the State legislators.
In certain colonies, the upper houses could (also) represent the interests of the mother country, selected by the governor.
Such views in support of bicameralism are now often considered less politically correct. More recently, bicameral systems with real powers for the upper houses are often found in federations, or quasi-federations, intended to give increased influence to (the smaller) regional states or provinces. Another pro-bicameralism argument is that it increases "checks and balances" on the government. Regardless, in non-federations, there have been a tendency towards unicameral system, or, if keeping a bicameral system, removing effective power from the upper house.