Definition:Center


 * Analysis:
 * Center of a power series


 * Abstract Algebra:
 * Center of a group
 * Center of a ring


 * Geometry:
 * Center of a circle
 * Center of a sphere


 * Graph Theory:
 * Center of a tree


 * Topology and metric spaces:
 * Center of an open ball

Linguistic Note
British English spells this centre.

The convention on is to use the American English spelling center, but it is appreciated that there may be lapses.