Source-code compatibility (source-compatible) means that a program can run on computers (or operating systems), independently of binary-code compatibility and that the source code is needed for portability.
[1] The source code must be compiled before running, unless the computer used has an interpreter for the language at hand.
[2] The term is also used for assembly language compatibility, where the source is a human-readable form of machine code that must be converted into numerical (i.e. executable) machine code by an assembler.
[3] Source compatibility is a major issue in the developing of computer programs.
For example, most Unix systems are source-compatible, as long as one uses only standard libraries.