Amalgam comics
A series of one shots in the late 90s jointly published by Marvel and DC comics, depicting a world where the Marvel and DC universes have merged. The Amalgam universe was created during the Marvel vs DC crossover. Meta-fictional letters pages and other materials such as a trading card set built on the conceit that Amalgam comics had a rich history and had been published for decades.
Continuity
One of the biggest debating points in comics. The consistency of characteristics, and, especially regarding comics, the consistency of prior stories.
Crisis
Short for Crisis on Infinite Earths. Comics first mega crossover. Published by DC comics, this story attempted to sort out all the varying and contradictory parallel worlds in the DC multiverse. It was arguably successful in this task.
Elseworlds
A now defunct imprint of DC comics, which has stories of DC characters in alternate settings. The stores often but not always have DC heroes in different historical settings such as the old west, medieval times, WWII, 1920s, or the Victorian era. Some have settings in famous literature, such as Superman/War of the Worlds, Batman/Dracula, Batman/Frankenstein, etc.
Hypertime
A concept introduced in 1999, in DC comics miniseries The Kingdom. The idea is that any story ever published actually occurred somewhere in DC's multiverse. To quote Mark Waid "It's all true. Basically think of a river with different tributaries. There is a mainstream DC universe. Any stories that ever contradicted something in the mainstream universe is in a different branch, or tributary, and may or may not rejoin the main stream at some point.
In continuity Crossover
A crossover that has "really happened" in the continuity of one or both worlds. The events of the story will be referenced and/or affect future stories of one or both worlds.
Marvel 616
The numerical designation for the fictional world portrayed in most Marvel comics. The term was first coined by Alan Moore and Alan Davis in a July 1983 issue of The Daredevils anthology comic, published by Marvel UK. The story was called Rough Justice, about the Captain Britain Corps. In the story the term is used to distinguish the mainstream Marvel reality from other Marvel realities, such as ones portrayed in the series What If, for example. Since then numerous American Marvel publications have adapted the phrase. Much speculation has gone into why Alan Moore chose the number 616, but it's possible it was chosen at random. Alan is usually credited with creating the term, but Alan Davis claims it was first used by previous UK comics Captain Britain writer David Thorpe. According to Davis, Thorpe chose this number as an allusion to the number of the beast.
Post Crisis: The DC universe as known after the 1985 miniseries Crisis on Infinite Earths.
Pre Crisis
The DC Universe as known prior to the 1985 Miniseries Crisis on Infinite Earths.
Public Domain
Fictional characters for whom the trademark and copyright have lapsed, hence are no longer, and can no longer, be owned by any one company or individual. For example, Dracula is public domain, hence any one can legally make a Dracula book, movie, comic, etc. Different countries have different laws regarding public domain. Most laws relate to a certain passage of time after the original publication, and/or the authors death.
Unofficial Crossover/Out of continuity crossover
A crossover that is done just because. The story has no bearing on either set of characters real worlds. Probably most crossovers fall into this category, but that is debatable.
