In FreeBSD, you have two parts of the operating system:
1.) the base system
This is your operating system itself (the kernel, grep, ls, along with other commands and some useful utilities). They are divided into different versions -- e.g. 8.0, 8.1, 8.3, 8-STABLE, 9.0, 9.1, 9-STABLE, 10-CURRENT and so on.
2.) ports
These are the third party utilities/programs, and don't affect the base system whatsoever, but they do change the user experience quite a bit. Since ports are just a collection of Makefiles and patches, and you build them from source, they can (in theory) work in any FreeBSD version (in practice they build on those versions of FreeBSD that are still supported and have not yet reached EOL -- so some ports may not build on FreeBSD 10-CURRENT, 9.0, 8.0, 7.* ...).
In your case, current is referring to the latest revision of the ports tree (which again, has connection to the FreeBSD 10-CURRENT).