Reformatio in peius

Reformatio in peius (from Latin reformatio, 'change' - actually, 'improvement', and peius, 'worse') is a Latin phrase used in law meaning that a decision from a court of appeal is amended to a worse one.
Prohibition of reformatio in peius at the European Patent Office
Under the case law of the Boards of Appeal of the European Patent Office (EPO), a Board cannot put a sole appellant in a worse position than if he had not appealed the first instance decision. Hence in relation to appeals, the term "prohibition of reformatio in peius" essentially means that a person should not be placed in a worse position as a result of filing an appeal. Thus, in general, EPO Boards of Appeal are prevented in opposition appeal proceedings from going beyond the request of a sole appellant to put it in a worse position than it was before it appealed. The central case detailing this principle is G 4/93 consolidated with G 9/92.
This principle...