Astrophysics has a tradition of using the word code much as much as others would use the word program (i.e., computer program). (This usage of the word code is also seen in physics and in engineering fields using advanced physics.) In astrophysics, code can mean a computer program or computer subprogram (i.e., procedure or subroutine) or library of subprograms. This usage appears most often for computer programs that simulate or model physical processes, e.g., radiative transfer code for radiative transfer. Outside this astrophysical usage, code is commonly used as a mass noun, indicating the substance of a computer program, e.g., "I'm adding some code to my computer program this month", or "I wrote a computer program this month", but not "I wrote a code this month". In astrophysics usage, it is sometimes used in the latter manner, i.e., you can indeed speak of "a code" or "two codes".