A casualty report, or casualty list, is a list of officers who have been killed, injured, or reported missing. Such reports are usually filed following a major military conflict.
During the Dominion War, CaptainSisko had the grim honor of posting weekly casualty reports in the wardroom of Deep Space 9. They were usually posted on Fridays. There was a time when every week brought sorrow to the station as the crew began finding old friends and acquaintances' names on the reports. He always made sure he read the names, feeling it was the least he could do for the men and women who had lost their lives.
DoctorBashir and CommanderDax often discussed whom they had lost each week. One week when the only recognizable name on the list was a friend of a friend of Dax's, Bashir observed that, considering recent events, it was a good start for the week.
After a particularly bloody battle at AR-558 later that week, Captain Sisko gained a new appreciation for the names on the casualty report as the names on the list came to life. (DS9: "The Siege of AR-558")
A casualty report may also be given as an update to the status of the crew when casualties occur during a situation instead of afterward. After Captain Hikaru Sulu asked for a damage report, Janice Rand reported nineteen wounded from the incoming casualty reports. (VOY: "Flashback")
In VOY: "Imperfection", Seven viewed a casualty list detailing all the members of Voyager's crew that had died thus far. It listed many names that had not been mentioned in the series and it is possible these were the crewmen that perished during the rough trip to the Delta Quadrant. One of these names could be the unnamed doctor played by Jeff McCarthy or the unnamed and unseen engineer, both who perished in VOY: "Caretaker". In actuality, most of these names listed are in-jokes referring to the characters of The West Wing. At the time the episode aired, West Wing and Star Trek: Voyager shared the same timeslot on different networks.
A large, detailed casualty report was created for the final years of DS9, depicting numerous casualties by ship. The graphic was created in a small format for Sisko's PADD (seen onscreen in "The Siege of AR-558" and "What You Leave Behind"), and a larger wardroom display (seen in "In the Pale Moonlight") that was capable of being rearranged to show new Romulan and Klingon ship and personnel names in later battles after alliances were formed (as seen in "Image in the Sand" and "The Siege of AR-558"). The smaller version was reproduced in the Star Trek: Deep Space Nine Companion. This is how we know the various Starfleet officer names listed in all three formats, as comparison between the three versions always yields the same Starfleet names listed in the same order. Some names are duplicated from ship to ship, and in the later revision, some Romulan and Klingon ships have their own personnel listed, but some show that Starfleet personnel are among the allied crews.