A fairth was an image or likeness produced by magic. It was created by mentally capturing the image one was currently intensely picturing and using magic to transfer it onto a surface, usually a slate tablet, with colored pigments imbued in it. Young Dragon Riders often did this to practice controlling their mind with great precision. It showed how well the rider was paying attention to all things, not just one.
Oromis' fairths Edit
Eragon's fairths in Eldest Edit
Usually, riders comprised an incomprehensible image the first time. Eragon, however, created an image that was focused on one thing first and the surroundings were unfocused and blurred. It was an image of sap on a broken bough. It was possible to create a false image with a fairth, though it is very difficult: usually only a very experienced Magic user could do this. Oromis taught Eragon how to do this and Eragon created a fairth, accidentally expressing his romantic feelings for Arya. Unluckily, he did so in front of her and when she saw it, she became frustrated and broke the fairth, causing the image upon it to vanish. This led to Oromis and Eragon discussing the implications of his actions and Eragon also began to understand better how his passion for Arya could not be realized at that time.
Eragon's fairth in InheritanceEdit
Towards the end of Inheritance Eragon makes another fairth of Arya (During his first encounter with Fírnen). This time he manages to create an image that portrays Arya not just as a subject of beauty but as a being with flaws and fears. He tosses the fairth to shatter it but Arya stops it in mid-air before it falls. Upon seeing the fairth Arya is surprised and says that in time they may become more than just friends.