GCC is the GNU Compiler Collection. It's the de facto standard C compiler on Linux and supports many other languages and platforms as well.
GCC includes a C compiler that is the standard C compiler on Linux. GCC also includes front ends for C++ (including a large amount of experimental support for C++11), Objective-C, Fortran, Java, Ada, and Go, as well as libraries for these languages (libstdc++, libgcj,...). It supports many architectures.
See also GCC online documentation.