Ports provide a simple way to install applications to freebsd from source code. The ports collection uses Makefiles arranged in a directory hierarchy so that software can be built, installed and uninstalled with the make command.
As of April 2013 there are more than 24.000 ports available.
FreeBSD Website: http://www.freebsd.org/ports/
FreeBSD Handbook: http://www.freebsd.org/doc/en/books/handbook/ports-using.html