A comb was a small object with multiple narrowly-spaced projections called "teeth", used to style hair.
In 2370, Benjamin Sisko said he and Jadzia Dax had combed through data on uninhabited Class M planets in the sector surrounding Deep Space 9, and found Draylon II to be a possible new homeworld for the Skrreea. (DS9: "Sanctuary")
To go over something with a fine tooth comb was a metaphor for looking it over extremely closely and carefully. In 2371, Captain Kathryn Janeway instructed Tuvok to tell B'Elanna Torres to go over damaged sensor logs with a fine tooth comb. (VOY: "Cathexis")