A more thorough explanation:

Term: In cursu rebellionis
Definition: In the course of a rebellion. This term was used in the past to describe a legal situation where a person who had not fulfilled a civil obligation was considered to be in rebellion against the Crown. This meant that their property could be taken by the Crown, they could be put to death without consequence, and they lost all their legal rights. If the person remained in this state for a year and a day, they were considered "civiliter mortuus" or legally dead, and their property would revert to their superior. This legal concept was abolished by a law in 20th century.
Example: In the past, if someone owed money to the government and did not pay it back, they could be declared "in cursu rebellionis" and lose all their property and rights. For example, if a farmer owed taxes to the Crown and did not pay them, the Crown could take their land and animals. If the farmer remained in this state for a year and a day, they would be considered legally dead and their property would go to their landlord. This law was very harsh and was eventually changed.