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, 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