Answer:
a way in which something is usually done, especially within a particular area or activity."the woman who overturned so many conventions of children's literature"
OR.
an agreement between countries covering particular matters, especially one less formal than a treaty."the convention, signed by the six states bordering on the Black Sea, aims to prevent further pollution"
Explanation: Depends on what your using it for. Similar words:
agreement /
accord /
protocol /
compact /
pact /
treaty /
concordat