Quills, short for quils pen, are ink pens made from the feathers of a bird in our world. In the world of fantasy RPGs like D&D, a magic quill is needed for making scrolls that have magic spells. Quills for inscribing these come from magical creatures, like gryphons or pegasi. Some such quills might be collected by elves and then sold for a high fee. Other quills might come from more dangerous creatures that require the creature to be tracked down and slain to collect all its feathers, not just the ones that fall to the ground.

For some DMs, a single feather can be used to scribe a single scroll or a single page in a spell book.

It all depends on how the DM wants things to work in his campaign. Some DMs may not worry about this aspect of it, or it may only be an issue for making scrolls, or only for the most powerful of spells.