(topology, mathematical analysis, restricted to metric spaces) The set of all points in a metric space whose distance from a given point ("the open ball's center") is less than a given length ("the open ball's radius").

(mathematics) A rectangle in the real plane which is an open set: i.e., which does not contain its edges. If the sides of the open rectangle are parallel to the plane's axes, then the open rectangle can be described as the Cartesian product of two open intervals.

(mathematics) An interval in the real line which contains one of its endpoints but not the other one: i.e., it either contains its supremum or its infimum but not both.

(mathematics) an interval in the real number line which does not contain its supremum and infimum. If specified by a pair of real numbers, then it consists of all the points on the real line whose values lie strictly between those two real numbers.

plural of open set

(topology) A cover whose members are all open sets.

(Christianity, somewhat colloquial) religious to the point of excess; ridiculously religious

(mathematics, functional analysis) An operator L such that for functions f and g and scalar λ, L (f + g) = L f + L g and L λf = λ L f.

plural of pipe-opener

A system of circulation which is achieved primarily from the heart beating and muscle-induced locomotion of the organism, circulation without veins.