The United States Senate requires a supermajority of 60 percent to move to a vote through a cloture motion, which closes debate on a bill or nomination, thus ending a filibuster by a minority of members. There are currently 100 members, so sixty percent is sixty Senators.
The United States Constitution requires a supermajority of two-thirds of both houses of United States Congress to propose a Congress-driven constitutional amendment; it also requires a three-quarters supermajority of state legislatures for final adoption of any constitutional amendment, as well as a two-thirds supermajority to pass a bill over the president's veto.
A two-thirds majority is a common supermajoritarian requirement in elections, especially whenever minority rights can be changed (e.g. constitutional amendments). There are two kinds of two-thirds majority: the simple or the absolute.
A two-thirds majority means that the number of votes for a proposition or candidate must equal or exceed twice the number of votes against it. If unqualified, two-thirds majority by itself always means simple two-thirds majority.
An absolute two-thirds majority means that two-thirds of the entire membership of a body or more must agree to the proposition. It is much stronger than a simple requirement.
Majority of the entire membership
In parliamentary procedure, another type of supermajority is a majority of the entire membership that is based on the total number of voting members of the society. It is any number more than one half of the total number of members.
To illustrate, if the society has 35 members a majority of the entire membership is more than 17.5 votes (usually 18, unless there are fractional votes). If only 20 members attend, a motion receiving 17 votes for adoption would not meet this requirement, even if the other 3 members chose not to vote, i.e. abstained.
Some parliamentary authorities, such as Robert's Rules of Order use a majority of the entire member as an alternate method to Rescind or Amend Something Previously Adopted or to adopt special rules of order.
Majority of the fixed membership
A majority of the fixed membership is a supermajority that is based on the total number of the established fixed membership of the deliberative assembly. It is used only when a specific number of seats or memberships is established in the rules governing the organization, e.g. a board of seven members.
This majority of the fixed members is set at any number greater than one half ot the total possible memberships or seats. For example, on a 7 member board, the majority of the fixed membership is 3.5 (usually 4 votes). For something to receive a majority of the fixed it would have to receive more than 3.5 votes. If the board had 4 vacancies, and only three members remaining, it would be impossible for any motion to receive a majority of the fixed membership, even if all three members voted in favor of it.
Most private organizations do use this standard. The popular parliamentary manual, Robert's Rules of Order, does not require it for any action. It is sometimes the stardard set to adopt some or all actions in state and local government legislative bodies in the United States.