A necrology is a list of people who have died, or an obituary of a single person. If someone is writing a history of one battle of the Civil War, they might attempt a necrology of every soldier who died.
If the newspaper publishes a list of passengers who died in a plane crash, you can call it a necrology. And the obituary, or death notice, of your great grandfather who died at the age of 110, can also be called a necrology — although obituary is much more common. Necrology was used more often in the eighteenth century, and it comes from necro-, "death," from the Greek nekros, "corpse."