NTSC fix
Adapting a demo written for PAL machines so it also runs on NTSC — the scene's most stubborn compatibility problem.
European home computers used PAL, American ones NTSC, and the difference was more than frame rate. On a Commodore 64 an NTSC machine has fewer raster lines per frame (262 against 312), a different number of cycles per line and partly different badline behaviour. Code that counted cycles exactly — and all raster-timed demo code did — crashed or flickered when run on the "wrong" machine.
An NTSC fix was the extra work of making a production behave on both. Sometimes adjusted delays sufficed; sometimes it took wholly separate code paths that detected the machine type at start-up. Because the scene was European, PAL was the norm and NTSC an afterthought; a release marked "NTSC-fixed" was a courtesy to a minority of users, and never a given.