What is Ordinance Of 1787?

Legal Definition
An act of congress which regulates the territories of the United States. It is printed in 3 Story, L. U. S. 2073. Some parts of this ordinance were designed for the temporary government of the territory north-west of the river Ohio while other parts were intended to be permanent, and are now in force. 1 McLean, R. 337; 2 Missouri R. 20; 2 Missouri R. 144; 2 Missouri R. 214; 5 How. U. S. R. 215.
-- Bouviers Law Dictionary