Quiver

From DwarfFortressWiki

A Quiver is an item needed by marksdwarfs, hunters, or anyone else that intends to wield a crossbow or bow. The quiver will hold a number of bolts or arrows for the character to fire. A quiver is typically made of leather.

Dwarves cannot use bows, but can use crossbows. In adventure mode, where you can make a human or elf, both of those races can use bows. Either way, they need a quiver to hold their respective ammo.