A strategic victory is a victory that brings long-term advantage to the victor, and disturbs the enemy's ability to wage a war. When a historian speaks of a victory in general, it is usually referring to a strategic victory.
For example, during the American Civil War, Union and Confederate armies fought each other at the Battle of Antietam. The battle was tactically inconclusive. Both armies suffered about the same amount of casualties, however it brought the Confederate invasion of Maryland to a halt, and caused Britain and France to abandon plans to potentially recognize the Confederacy as a legitimate government. By preventing these events which would have seriously damaged the Union cause in a wider sense, the battle is therefore generally recognised as a strategic victory for the Union forces.