Illustrated Glossary of Organic Chemistry

Stereocenter (chiral center): An atom with three or more attachments, interchanging of two of these attachments leads to another stereoisomer. Most commonly, but not limited to, an sp3 (tetrahedral) carbon atom bearing four different attachments.

sp3 carbon
                stereocenters
sp2 carbon
                stereocenters

Sulfur and
                nitrogen stereocenters
Stereocenters at sp3 carbon
  
Stereocenters at sp2 carbon
  
Sulfur and nitrogen stereocenters