Antialias Document

Selecting Render > Antialias Document smooths rough edges in your Document view for preview purposes. Antialiasing is a process of oversampling image data to smooth object edges and avoid a jagged appearance along them. The following images show a test render both without (left) and with (right) antialiasing enabled.

Normal preview (left); Anti-aliased (right).

You can specify whether or not to apply antialiasing during renders when specifying render settings. Please refer to The Render Settings Dialog for more information about specifying render settings.