Nine votes are necessary, but sometimes not sufficient
The Security Council has fifteen members. Substantive decisions require at least nine affirmative votes and cannot pass if one of the five permanent members casts a negative vote. The permanent members are China, France, Russia, the United Kingdom and the United States.
This is the veto in practical terms: a permanent member does not need to persuade a majority to stop a substantive resolution. It needs to vote against it.
Abstention is different
A permanent member can abstain without preventing adoption if the resolution still receives the required nine affirmative votes. That distinction allows a government to distance itself from a decision without necessarily blocking the Council.
Procedural matters follow a different rule and require nine affirmative votes without the same permanent-member veto structure.
The veto converts status into bargaining power
Because each permanent member can block substantive action, draft resolutions are often negotiated with veto positions in mind before a vote occurs. The visible veto is only the clearest expression of the power; anticipated vetoes can shape language and diplomacy earlier in the process.