Originally an Acronym for "GNU C Compiler", now a Backronym for "GNU Compiler Collection".
A collection of compilers for C, C++, Fortran etc. The compilers aim to be first and foremost standards-compliant and correct. This differs from other compilers many of which are developed by commercial companies and specialised to show off their hardware or software.
Java support (GCJ) is a new and not yet robust.
The Compiler that the Linux kernel is normally built with and the one that ships as standard on most GNU/Linux systems.
See also: http://gcc.gnu.org/ (not http://www.gcc.org), gcc(1), cpp(1), as(1), ld(1) and gdb(1). Also check out this GCC Forum hosted by Nabble which archives all gcc mailing lists into a searchable forum.