A shoehorn was a type of tool used to assist wedging one's heel into a shoe. As a verb, the term was used in a more figurative sense to refer to packing someone or something into a space that wasn't large enough for it to comfortably fit inside.
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." (VOY: "Drone")