A breach or disturbance of the peace is an activity in a public place that might reasonably be expected to disturb or upset others. Breach of the peace is generally treated as a misdemeanor, and sometimes the person committing it will only be given a warning, asking that he or she cease the activity in the interests of keeping public order. Many nations have laws pertaining to such disturbances on their books, and they are interpreted and used in different ways.
The idea of a breach of the peace comes from Commonwealth nations where there is a monarch. Historically, the King or Queen's peace was a right that was supposedly extended to all citizens living in the monarchy; disturbances of the peace were regarded as a disturbance of the monarch, as well as an offense to the dignity of the nation. In several monarchies, these laws are actually quite strict, as seen in the Public Order Acts used in Britain to suppress a variety of activities.
Things which might be considered a breach of the peace can include getting into fights, singing loudly, being drunk and disorderly, and engaging in other loud or disruptive behavior. In some nations, it must constitute a threat of some kind; beyond simply being upsetting, it must be something that causes people to fear for their safety. In others, generally loud, disruptive, or obnoxious behavior may be grounds for a warning or arrest by law enforcement officers, who are charged, among other things, with keeping the peace.
In some cases, breach of the peace laws can be used to quell demonstrations that do not have permits. The argument here is that when a march is permitted, the community has time to prepare, and the event is not considered a legal disturbance because it is occurring by arrangement. A spontaneous or unpermitted demonstration, however, might pose a threat to safety and comfort, and thus could be disbanded under breach of the peace laws, depending on the nation.
In some cases, someone who is disturbing the peace may be taken into custody. This is often done when there are safety concerns, as for example when someone who is intoxicated is wandering in the street. People can also be fined or ordered to do public service as a penalty for breaching the peace, with such punishments usually occurring after multiple warnings have been given.