Source port
From ZDoom Wiki
Source port is the term used for any source modification of a game created by the game's community. This term may have been based on the fact that the Doom source code was originally released for Linux, and had to be "ported" to other operating systems, most notably DOS and Windows. The original purpose of Doom source ports was cross-platform compatibility, but shortly after the Doom source release, programmers were correcting old, unaddressed Doom bugs and deficiencies in their own source ports, and later on adding more features to alter gameplay, add new features, and so on. ZDoom is one such source port.
NOTE: Other older games may have source ports now, even though the above paragraph may have implied "source ports" were limited to Doom (e.g. Duke Nukem 3D has several source ports).
