Definition:Center


 * Analysis:
 * Center of a power series


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


 * Geometry:
 * Center of a circle
 * Center of a sphere
 * Center of a conic section
 * Center of curvature of a curve at a point


 * Graph Theory:
 * Center of a tree


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