A mission log was a log which recorded the events of a specific mission.

Gabrielle Burnham kept a mission log of her time travel experiences using the red angel suit, recorded on two mission log drones, saved to a data module within the suit. Lieutenant Paul Stamets and Ensign Sylvia Tilly were able to download the logs in 2257, for Michael Burnham to review. (DIS: "Perpetual Infinity")

In 2367, Data ordered the computer to scan all isolinear chips containing mission logs aboard the Onizuka, but found no discrepancies. (TNG: "The Mind's Eye")

In 2368, in order to discover a connection between a group of Ullians and cases of unexplained comas, Geordi La Forge searched the Ullians' mission logs; he discovered that when two such cases had occurred in the Epsilon Nel system, Tarmin had been on the Ullian homeworld, so could not be responsible. (TNG: "Violations")

In 2369, an explosion aboard the USS Yosemite scrambled all logs aboard the ship, including mission logs, science logs and medical logs. (TNG: "Realm Of Fear")

In 2375, the Silver Blood copy of the USS Voyager planned to launch a probe containing the ship's records, but the probe was destroyed before its launch, so everything including personal logs and mission logs was gone. (VOY: "Course: Oblivion")