General explanations including specifics regarding Wolf3D modding.
General
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.
Mod
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.
Add-On
Old term and barely anyone uses this one anymore. It's usually adding more content to the original mod or game but rarely has all the necessary files to run on its own. Adding only a small amount of new content. Classic add-ons for games were sort of like DLCs for modern games but with a bit more content.
Map Set
As the name says it's most of the times just a set of new levels.
New Game
Very advanced mods or rather total conversions that turned into standalone games and don't have much in common with the original Wolf3D anymore except for the engine. Total conversion sometimes blur the lines between the worlds and it depends on what defines a new game unless.
Patch
Usually patches are small files made to fix some bugs or glitches of a mod or game. 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.
Registered
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 the 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 compability 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.
Source Ports
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 what point it stops being a TC and turns 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.