plural of open cluster

(uncountable) A chess opening characterized by the moves 1.e4 e5, in which both White and Black move their king's pawn to the fourth rank with their first move.

plural of open game

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

(education) Referring to exams in which external resources such as textbooks, glossaries, study notes, calculators, etc. may be used.

(idiomatic) Something of which salient aspects are obvious or easily interpreted.

plural of open door

(idiomatic) To lead to opportunities or (social) advantages.

(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").

plural of open verdict