A more thorough explanation:

pro omni alio onere

Pro omni alio onere is a legal term that means "for every other burden." It refers to a clause in a charter that limits a vassal's duties to only those that are specifically listed in the charter. This means that the vassal is not responsible for any other obligations or duties that are not explicitly stated in the charter.

For example, if a vassal's charter states that they are responsible for providing military service and paying taxes, but does not mention anything about providing food or shelter for the lord, then the vassal is not obligated to provide those things. Pro omni alio onere ensures that the vassal is only responsible for what is explicitly stated in the charter and not burdened with any additional duties.