The centre of a circle is the point equidistant from the points on the edge. Similarly the centre of a sphere is the point … See more

For objects with several symmetries, the centre of symmetry is the point left unchanged by the symmetric actions. So the centre of a square, rectangle, rhombus or parallelogram is where the diagonals intersect, th… See more

Several special points of a triangle are often described as triangle centres:
• the circumcentre, which is the centre of the circle that passes through all three vertices;
• the centroid or centre of mass, the point on which the tr… See more

A tangential polygon has each of its sides tangent to a particular circle, called the incircle or inscribed circle. The centre of the incircle, called the incentre, can be considered a centre of the polygon.
A … See more

The centre of a general polygon can be defined in several different ways. The "vertex centroid" comes from considering the polygon as being empty but having equal masses at its vertices. The "side centroid" c… See more

In projective geometry every line has a point at infinity or "figurative point" where it crosses all the lines that are parallel to it. The ellipse, parabola, and hyperbola of Euclidean geometry are called conics in projective g… See more

• Centrepoint
• Chebyshev centre
• Fixed points of isometry groups in Euclidean space
• Instantaneous centre of rotation… See more