Bicubic zoom

The images below are examples of the difference between bicubic- and linear zooming. Bicubic zoom is set to 'automatic' by default, see Settings, Image display. 'Automatic' means, that if bicubic zooming takes too much system resources, it'll switch to linear zooming automatically.
Linear zooming just enlarges the pixels, while bicubic zooming uses an interpolation algorithm to render the image.