What does "frankpledge" mean?

Frankpledge: (a) A pledge or surety for the good behavior of freemen, -- each freeman who was a member of an ancient decennary, tithing, or friborg, in England, being a pledge for the good conduct of the others, for the preservation of the public peace; a free surety. (b) The tithing itself. Bouvier. The servants of the crown were not, as now, bound in frankpledge for each other. Macaulay.