General explanations including specifics regarding Wolf3D modding.
ID Software permits modding and has released the source code on July 21, 1995. The official level editor ted5 has also been released although by 3D Realms in 1995. Modding is officially allowed with the exception to not infringe copyrights or trademarks of Bethesda/Zenimax/id Software. One example that got shut down due to this is Beyond Wolfenstein 2 SE.
id Software noticed the possible love for modding too late and didn't prepare Wolf3D for easier modding access but would do so with Doom. Due to the file structure of Wolf3D this has been a big issue for mods even if the mod was adding just a new enemy skin. ECWolf and LZWolf are allowing partial file changes now.
Short for modification and a very popular term all across gaming communities. Basically anything that modifies the original game in one way or another can be considered a mod. A quite broad description that sums up all the other classes.
Old term and it's barely used these days. It's usually adding more content to the original mod or game but rarely has all the necessary files to run on its own. Classic add-ons for games were sort of like DLCs for modern games but with a bit more content.
A set of maps replacing the original maps. The focus is on level design and usually doesn't add much feature-wise or resource-wise to the game outside of it. Such type of mods might come only with gamemaps.wl6 and maphead.wl6 data files. Very old sets might come with a maptemp file instead while ECWolf/LZWolf sets might come only with a pk3 file.
Very advanced mods, total conversions which have turned into standalone games, and don't have much in common with the original Wolf3D anymore except for the engine. Total conversions sometimes blur the lines between the worlds and it depends on what exactly defines a new game.
Patches are often small files made to fix some bugs or glitches of a mod or game. Basically patching up something, hence the name. In some cases the term also describes small type of mods that barely change anything of the game and just replace some resources. For example swapping the graphics of one enemy for a new one.
A big part of the mods are using the structure or files based on the registered version, also known as full version, of Wolf3D. This gives modders more resources and features, like extra enemy types, to work with. If such type of mod doesn't have all files needed to run it on its own one has to add the fitting files from the original game. Sometimes this ends in broken compatibility as the VGAGRAPH or the exe file can differ depending on the Wolf3D version. Most often mods are based on version 1.4 but there are exceptions.
For mods this means they are usually building upon the demo/shareware version of Wolf3D, which was given away for free or for a little charge. Commonly they have less of everything (e.g. less enemy types, 10 levels) and very, very rarely have source code change. Such sets can be usually recognized at the "WL1" file extension. Many early mods are making use of this version.
Fans took the source code of the DOS version of Wolf3D and made the game compatible with various systems or specific features. Any mod that doesn't rely on the exe should be working in any port of the game. There are exceptions like Temporary Insanity which makes use of very specific bugs in the DOS version. Many Wolf3D mods rely on code changes and therefore their very own exe. They only run on their very own version and would have to be ported one by one.
Total Conversion (TC)
A term that is slowly fading into obscurity and is not often used as of 2019. As the name already says, it's a full conversion of the game and a very distinct type of advanced mod. It replaces all or almost all of the original game and can result in a very different type of gameplay as well. A sub-type would be a partial conversion, which replaces only large parts of the game. Total Conversions can turn into new games on their own and blur the lines between what is still a mod or a fully new game. Questionable is also at which point it stops being a TC and transforms into a new game. If it's the amount of changed resources or if the use of copyrighted material plays a role in it. Depending on what defines exactly a new game even a TC with copyrighted resources could still fill in the shoes although in a more illegal way.