Partial conversion

A partial conversion is a PWAD that replaces a portion of the resources of the original game's IWAD. In contrast to a total conversion, the partial retains enough visuals, sounds, and gameplay mechanics to be considered a variant of the original, not a separate game. The term was first used by the STRAIN project, which had a smaller scope of changes to Doom than Aliens TC or other prior total conversions.

One important factor distinguishes a partial conversion from a gameplay mod: custom maps. Partial conversions always have one or more custom maps combined with some gameplay changes. But gameplay mods only change gameplay. For example, the Monster Resource WAD has some of the custom STRAIN monsters. Using these custom monsters with a vanilla map is considered a gameplay mod, not a partial conversion.

To complicate matters, the community has a history of using the term loosely. For example, Back to Saturn X billed itself as a partial conversion, when in fact it is a mapset with custom textures. Since maps with custom textures are quite common, it is not generally accepted as a partial conversion anymore.