The abbreviation HPC stands for high-performance computing. This is an area of computer science dedicated to the development of programs that can handle large problems, like weather prediction with a very fine resolution. Typically it involves multiple processors, clusters of computers cooperating in the computation and specialised constructs in or dialects of standard programming languages (such as Fortran, C, C++).
Techniques involved: MPI (message passing interface), OpenMP, multithreading, GRID computing.