The crime of aggression was (in theory) added to the jurisdiction of the International Criminal Court in 2010 with its description in the so-called Kampala amendment. However its definition as well as conditions of exercise of jurisdiction are highly controversial, including the annex of resolution RC/Res. 6 encompassing the Understandings.
International Treaty Law doesn't know the term understandings and neither does the Rome Statute. This article thus describes their status and role.