Complex sentence: For programs, this generally means that it is written in a metalanguage that can be read by any ported, i.e. the code can be adapted for a certain platform and compiled for the platform it will be functioning in.
Split into simpler sentences: For programs, this generally means that it is written in a metalanguage that can be read by any platform. A program that was not originally written for a certain environment can be ported, i.e. the code can be adapted for a certain platform and compiled for the platform it will be functioning in.