Русско-англо-русский юридический словарь

A supermajority, or a qualified majority, is a requirement for a proposal to gain a specified level of support which is greater than the threshold of one half used for majority. (Wikipedia)

Supermajority rules say that an agreement by a designated majority (in terms of the aggregate number or size and typically different from a simple majority) is binding on all members. (International Bank Management, publisher: John Wiley & Sons)