A diary or journal was a form of personal log.
Sajen, a Suliban detained at the Tandaran Detention Complex 26 in the mid-22nd century, kept a journal. Travis Mayweather speculated that the journal might prove a valuable record of what had happened there one day, a thought Sajen dismissed. (ENT: "Detained")
Julian Bashir at one point gave his medical school diaries to Jadzia Dax, so she could better understand him. She considered keeping them when she believed him killed in 2370. (DS9: "Armageddon Game")
Lwaxana Troi diligently kept a journal since before she was married, except for one peculiar seven year gap. One bad experience she mentioned was the fact that her daughter was not married yet. (TNG: "Dark Page")
Erin and Magnus Hansen kept extensive field notes about their expedition to find the Borg, including extensive journals. This data set was at one point referred to as the "Hansen diaries". (VOY: "The Raven", "Dark Frontier")