MPI is a library, not a language. It specifies the names, calling sequences and results of functions or subroutines to be called from C/C++ or Fortran programs, and the classes and methods that make up the MPI C++ library. The programs that users write in Fortran, C or C++ are compiled with ordinary compilers and linked with the MPI library.

MPI programs should be able to run on all possible machines and run all MPI implementetations without change.

An MPI computation is a collection of processes communicating with messages.