What is "quasi-war"

The Quasi-War was an undeclared war fought almost entirely at sea between the United States of America and the French Republic from 1798 to 1800. After the toppling of the French crown during the French Revolutionary Wars, the United States refused to continue repaying its debt to France on the grounds that it had been owed to a previous regime. French outrage led to a series of attacks on American shipping, ultimately leading to retaliation from the Americans and the end of hostilities with the signing of the Convention of 1800 shortly thereafter.