The U.S. government boasts a two-house legislature, which is referred to as bi-cameralism and includes the Senate and the House of Representatives. There are approximately 540 people who make up the entire legislature.
The authors of the U.S. Constitution established the two-house legislature in order to separate power into units, which naturally provides a system of checks and balances. This ensures that one party does not gain too much power at one time.
As a prime example of bi-cameralism, both branches of the house must work together and it is believed that they have equal power. Even so, some people do refer to the Senate as the upper body, and the House of Representatives the lower body. However, these names were derived from the locations where each house first met.