To ratify a document means to sign or give formal consent to make it officially valid. The Constitution could not become our new law until all states had an opportunity to oppose or approve of this new form of government based upon the views of the inhabitants, in state conventions. Ratification only required that 9 states approve the Constitution for it to go into effect. The Delaware Convention approved the Constitution on Dec 7, 1787 in a 30-0 vote. New Hampshire was the 9th state to ratify the Constitution on June 21st, 1788.

More Info: www.archives.gov