A death toll was the number of deaths that resulted from an incident.
In approximately 3074 inside the Museum of Kyrian Heritage, a Kyrian named Quarren explained that 700 years ago, the warship Voyager was one of the most powerful vessels of its time. Armed with photonic torpedoes and particle weapons, it could wipe out an entire civilization within hours. However, on that particular day in history, they were lucky in that the death toll could've been much worse had there not already been an evacuation taking place by time Voyager had targeted their major cities. The evacuation resulted in thousands of lives being saved. A holoprogram titled The Voyager Encounter revealed that a bio-agent which was released via phaser beam into the atmosphere of the Kyrian and Vaskan homeworld resulted in 3,000 Kyrian deaths, however, according to Tuvok, the fatality rate would be 300,000 in one hour as the bio-agent was still dispersing through the atmosphere. By the Great War's end, bioweapons resulted in eight million deaths. (VOY: "Living Witness")