A more thorough explanation:

Festing-man is a historical term that refers to a bondsman or a surety. It was commonly used in medieval England.

Frankpledge was a promise given to the sovereign by a group of ten freeholders, also known as a tithing, ensuring the group's good conduct. This system was of Saxon origin but continued after the Norman Conquest. The members of the group were not liable for an injury caused by an offending member, but they did act as bail to ensure that the culprit would appear in court. They were bound to produce a wrongdoer for trial.

For example, if a person was accused of a crime, their frankpledge group would be responsible for producing them in court. If they failed to do so, the group would be fined.

Another example is if a person needed to be released from prison on bail, their frankpledge group would act as surety for them.

These examples illustrate how the frankpledge system worked to ensure good behavior and accountability in medieval England.