Wikipedia:Supermajority

A Wikipedia Supermajority poll is a process for attempting to ascertain if a Consensus may be established by voting when it is clear that a true consensus -- meaning an absence of dissent -- can not be achieved by discussion within a reasonable length of time. When possible, polls should not be used, deferring instead to consensus by discussion without voting.

Practice

 * "Wikipedia is not an experiment in democracy. Its primary method of finding consensus is discussion, not voting. In difficult cases, straw polls may be conducted to help determine consensus, but are to be used with caution and not to be treated as binding votes." &mdash;What Wikipedia is not

For some routine Wikipedia administrative tasks, supermajority voting is mentioned in guidelines or is traditionally invoked to ascertain when a rough consensus for an action (or an inaction) has been met.

The numbers are by no means fixed, but are merely statistics reflecting past decisions. Note that the numbers are not binding on the editor who is interpreting the debate, and should never be the only consideration in making a final decision.

Deadlock
When questions are deadlocked without true consensus and there are no compromise alternatives forthcoming, declaring a rough consensus from the majority opinion &mdash; or the traditional supermajority, when there is one, as in changes to the status quo like deletion &mdash; may be the only practical way to resolve the issue. Decision makers must use their best judgement to decide when the question has been given enough time. At some point additional discussion will yield diminishing returns.

Another way to resolve such a deadlock is through dispute resolution. Decision makers must use their best judgement to decide whether the extra time and effort involved in dispute resolution is worth it.