(mineralogy) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO₂·nH₂O.

The collaborative design of things, especially of open source software, through use of publicly shared design information.

Neither reflecting nor emitting light. / Allowing little light to pass through, not translucent or transparent. / (figuratively) Unclear, unintelligible, hard to get or explain the meaning of.

(obsolete, poetic) An area of darkness; a place or region with no light. / Something which is opaque rather than translucent.

(transitive) To make, render (more) opaque.

Crowdsourcing.

present participle of open

Pertaining to the start or beginning of a series of events.

An act or instance of making or becoming open. / A gap permitting passage through. / An act or instance of beginning. / The first performance of a show or play by a particular troupe.

Acronym of Organization of Petroleum Exporting Countries.