A short description of cross compiling would be the following term:
Cross compiling is the procedure for building a program for a platform different from the one on which the cross compiler runs. "Platform" does not only mean the hardware architecture but also software platforms, e.g. the process for building the GNU/Hurd operating system from sources on a running Linux for the same hardware architecture is also a cross compiling.
But "cross compiling" covers more than the short statement above. For using and building a cross compiler, you need to know more than only download the source ; ./configure ; make ; make install. Frequently, problems appear which you wouldn't expect if you just compile a package for your computer. A generic solution for arising problems would be correcting it by installing or compiling the needed libraries - but, mostly, this doesn't work with a program which has to be cross compiled.
Personally, I would describe this process at least recursive. You've got a source code of the famous program foo and you notice that it depends on library libfoobar. So, you get the source of this library, but then, you remember, the library itself depends on another library libbar...
As you notice, you firstly have to compile the package libbar, then you can correct the problems of library libfoobar and then, you can finally compile the original source of foo.
Don't get frightened - many programs you want to compile are well described or you may get help from the Internet, news groups or mailing lists from all around the world.
The programs used in this article have all been tested and compiled. Mostly, they include a patch which represents a workaround of problem xyz for the platform SEGA Dreamcast.