Definition:Segment


 * Geometry:
 * Segment of Circle: The part of a circle cut off by a straight line that cuts the circle into two parts.
 * Line segment: a straight line whose endpoints are both defined.


 * Order theory:
 * (Initial) segment: A subset of a well-ordered set defined as the set of all elements of a well-ordered set which strictly precede a particular element.
 * Weak initial segment: A subset of a well-ordered set defined as the set of all elements of a well-ordered set which precede a particular element.