A problem that has been posed in a field of study such as mathematics or theoretical computer science, but whose answer is not yet known.

(initially derogatory) A subgenre of speculative fiction or science fiction that emphasizes space travel, romantic adventure, and larger-than-life characters often set against vast exotic settings.

(idiomatic) A theatrical production, film, or program on radio or television depicting adventures of characters in the American Old West; a western.

Something that is in its beta stage, or being tested.

Pertaining to a product sold by merchants at a discount, because the item was returned but found not to be defective.

plural of open problem

Alternative spelling of openwork

Any of several forms of metalwork or needlework having decorative openings. / (mining) A quarry; an open cut.

(genetics) A sequence of DNA triplets, between the initiator and terminator codons, that can be transcribed into mRNA and later translated into protein.

alert and vigilant