Karl Berry Olaf Bachmann and many others.
Portability is a quality of the code that enables it to be built and run on a variety of platforms.
At the time, I was maintaining a proprietary program that ran only on SunOS 4. Once it built correctly, I started testing to see if there were runtime problems related to portability. If at all possible, it is better to write portable code to begin with. There are a large number of Unix-like systems in the world, including many systems which, while still running, can only be considered obsolete. While it is probably possible to port some programs to all such systems, typically it isn't useful to even try.