Editing Dungeons & Dragons Glossary (section)

=== O ===

; OD&D
: '''Original ''Dungeons & Dragons''''' - also "Old ''Dungeons & Dragons''". Among adherents of the OSR, the term has come to refer strictly to the edition represented by the 0e box set and the supplements, and often the Holmes ''Basic Set''. Among the broader group of old school fans, the term is often used more broadly, and includes the rest of the BD&D line. There is some controversy over which is is the proper usage.

; OG
: '''Old Geezer''' - the username of RPG.net poster Michael Mornard, who was a player in the original Castle Greyhawk campaign co-DMed by Gary Gygax and Rob Kuntz in the early 1970s.

; OGC
: '''Open Game Content''' - any material released under the Open Game License (OGL).

; OGL
: '''Open Game License''' - an open-source license released by Wizards of the Coast in 2000 that allows third party vendors to use Open Game Content (OGC), like the SRD. Commonly used in conjunction with the more restrictive d20STL until 2003. Proposed revisions to the OGL were leaked in early 2023 that met with significant backlash due to the negative impact it would have had on third-party publishers. The revision was scrapped, and a minor revision made instead. The fifth edition OGC was also dual-licensed under a Creative Commons license, but other publishers also reacted by using alternative licenses of their own, like the Open RPG Creative (ORC) license.

; ORC
: '''Open RPG Creatice license''' - an open-source license released by a Paizo and other RPG publishers as an alternative to the Open Game License (OGL).

; OS
: '''Old school''' - a general adjective used to describe the style of early role-playing games. While primarily used to refer to ''D&D'' and its variants, the term can be more broadly applied to any early games. Different definitions have different cut off times; some exclude 3.X, 2E, 1E, everything but 0e, or various finer distinctions (lines are often drawn at ''AD&D'' 2nd edition's ''Player Option'' books, or 1E's ''Unearthed Arcana'').

; OSR
: '''Old School Renaissance''' - also ''Old School Revolution'' or ''Old School Revival''; the recent surge in popularity of older roleplaying games and styles. While partially attributable to the death of Gary Gygax in 2008, earlier retro games like ''HackMaster'' and ''Castles & Crusades'' (2006) tapped into the same sentiment. While there is a no true center or uniformity of opinion, the public face of the group is a fairly cohesive collection of games, magazines, message boards, publishers, and blogs (the most prominent of the latter being Grognardia). Common themes, as articulated in Finch's ''A Quick Primer for Old School Gaming'', are megadungeons, sandbox campaigns, an emphasis on player rather than character skill, and a focus on rediscovering how the creators of the games actually played. There's a heavy focus on 0e, with a secondary focus on ''AD&D'', specifically the pre-''Unearthed Arcana'' 1st edition.