A ceasefire is a temporary stoppage of a war, for any of various reasons. Some may be do to a formal treaty, while others are due to a common understanding. For example, December 25, 1914, there was an unofficial ceasefire on the western front of World War I, known as the Christmas Truce. There was no treaty signed, and after a few days the war resumed.

References

World War I Christmas Truce by Thousands of German Soldiers http://www.rense.com/general46/cchr.htm