A small book bound in leather
Leather was a material made from the hide of some types of animals. One such example was buckskin.
Captain Jonathan Archer kept a small, leather-bonded book in his ready room aboard Enterprise NX-01. (ENT: "Fortunate Son")
In 2267, Spock described a sound he heard as "wood rubbing on some kind of leather." Gaetano believed it signaled a coming attack by the Taurus II anthropoids, but Boma disagreed, saying it could instead be a tribal rite. (TOS: "The Galileo Seven")
In 2367, to explain Benjamin Maxwell's behavior, Jean-Luc Picard surmised that the captain had become so used to his anger that he was comfortable with it, as one might be with old leather. (TNG: "The Wounded")
Leather was often used to make articles of clothing, particularly jackets. Amelia Earhart was wearing a leather jacket when she was found by Kathryn Janeway in a cryo-stasis chamber in 2371. (VOY: "The 37's")
The final draft script of TOS: "Shore Leave" described the Black Knight charging, horse-back, at Leonard McCoy as galloping "hell for leather."
The script for DS9: "The Assignment" described engineer Whatley as being "leather-faced".