A smooth variety over a field is an algebraic variety
whose structure morphism to
is a smooth morphism.
Over a perfect field, this is equivalent to all
local rings of the algebraic
variety being regular. Smooth varieties are also called nonsingular varieties.
The points at which an algebraic variety is smooth form its smooth locus. The remaining points are its singular points. In characteristic zero, a resolution of singularities replaces a algebraic variety by a smooth variety through a proper morphism that is also a birational morphism.