A more thorough explanation:

Breach of prison, also known as prison breach, refers to a prisoner's forcible breaking and departure from a place of lawful confinement. It is the offense of escaping from confinement in a prison or jail. In some jurisdictions, prison breach is distinguished from escape by the presence of force, but this distinction is not always followed.

For example, if a prisoner uses a tool to break open a window and escape from jail, it would be considered a breach of prison. Similarly, if a prisoner overpowers a guard and escapes, it would also be considered a breach of prison.

At common law, breach of prison was considered a felony, and even conspiring to break it was punishable. However, the severity of this offense has been mitigated by the statute de frangentibus prisonam, which states that no person shall have judgment of life or member for breaking prison unless committed for some capital offense. Therefore, breaking prison when lawfully committed for any treason or felony remains a felony, while breaking prison when lawfully confined upon any other inferior charge is punishable as a high misdemeanor by fine and imprisonment.