A shoehorn was a type of tool used to assist wedging one's heel into a shoe. The term was also used in a more figurative sense to refer to packing someone or something into a space that wasn't sized large enough for it to comfortably fit within.
During the 2360s Starfleet Academy would occasionally assign its cadets to class 2 shuttles for various training missions. According to Tom Paris, "they used to shoehorn half a dozen cadets into one of these things for weeks at a time," due to their size and lack of general comfort. (VOY: "Drone")