A breach of the peace refers to disturbing public order. This includes actions that could put people at risk, as well as simply upsetting the harmony of the community.
Breaches of the peace are considered unlawful and can be punished by fines and/or jail time. Some breaches of the peace are considered worse than others.
An example of a breach of the peace would be if someone were screaming obscenities in a public park. Another would be if a person were incessantly blowing an air horn on a sidewalk. Breaches of the peace can also include carrying unlawful weapons in public spaces.
Breaches of the peace do not necessarily involve violence, yet the public can still be in potential danger. An example of this would be if two groups of people were shouting at and threatening to fight one another.