Antialiasing is the process of removing or avoiding 'jaggies' or 'stairstepping' and other objectionable digital artifacts.
Antialiasing can be toggled most easily by going to the View menu and selecting Antialiased.
Fractal eXtreme's poster renderer and interactive antialiasing do antialiasing by calculating extra pixels and then averaging the results. This gives smoother curves, and effectively increases the resolution of the image. Because the averaged pixels can be virtually any colour, all antialiased images are saved as true-colour.