The Bezier Selection tool creates selection areas using bezier curves. Bezier curves are explained in greater detail in the Paths Dialog Help section.
Bezier Selection Settings
The Feather option sets the amount of selection feathering to create when rendering the selection. Feathering softens the edge of the selection by the specified number of pixels. See also: Feather Selection.
The Antialiasing button toggles the rendering of aliased edges on the selection boundary. Aliasing produces smoother curves and angles and is recommended for most uses.