Define lets you lookup words on the page of a book by using your iPhone camera to detect words instead of typing them.
To define a word, center that word in the viewport. Once the word has been detected, it will be highlighted in yellow and its definitions will appear at the bottom of the screen.
Some words may be difficult to detect using character recognition. If you find that the word youre attempting to define isnt being detected, try altering the angle of the camera when pointing it at the page.