You get the base system with a FreeBSD install. It includes the kernel and everything else that makes it a "FreeBSD system". This is stuff maintained by the BSD team. Everything else is an add-on.
This is why I typically find Debian to be a more cohesive system than FreeBSD. If I could run only the base system, or only the base system plus maybe one or two packages, FreeBSD would have a very good story about being developed in a unified, coherent way. But in practice I need a bunch of stuff from ports, and on FreeBSD that much more clearly falls into the "everything else is an add-on" category. There's relatively little integration testing or attempts to make the software in ports do things in a coherent "FreeBSD-style" way; it's a bunch of third-party software delivered mostly as-is. Whereas Debian considers anything in the 'main' Debian repository part of the official release, subject to release-management and integration testing, and ensures it works in a more or less "Debian way". Whether that matters depends on your use case, but for me that makes Debian feel more like a unified system.
I'm thinking mostly about servers here fwiw. On desktop the base/applications distinction works better for me, so I could run "FreeBSD" as a coherent base system and then install some separate applications on top of it, which is all fine. But on servers I prefer the coherent base system to be more "batteries included", including integrated release management of all the major libraries and software packages I'm likely to need. If I deploy on "Debian 8" vs. "FreeBSD 10", for example, the former gives me a much larger set of stable components that work together in a reasonable way, while the latter leaves me to more DIY it outside of the relatively small base system. (Whether this matters of course depends on what you're building.)
This is why I typically find Debian to be a more cohesive system than FreeBSD. If I could run only the base system, or only the base system plus maybe one or two packages, FreeBSD would have a very good story about being developed in a unified, coherent way. But in practice I need a bunch of stuff from ports, and on FreeBSD that much more clearly falls into the "everything else is an add-on" category. There's relatively little integration testing or attempts to make the software in ports do things in a coherent "FreeBSD-style" way; it's a bunch of third-party software delivered mostly as-is. Whereas Debian considers anything in the 'main' Debian repository part of the official release, subject to release-management and integration testing, and ensures it works in a more or less "Debian way". Whether that matters depends on your use case, but for me that makes Debian feel more like a unified system.
I'm thinking mostly about servers here fwiw. On desktop the base/applications distinction works better for me, so I could run "FreeBSD" as a coherent base system and then install some separate applications on top of it, which is all fine. But on servers I prefer the coherent base system to be more "batteries included", including integrated release management of all the major libraries and software packages I'm likely to need. If I deploy on "Debian 8" vs. "FreeBSD 10", for example, the former gives me a much larger set of stable components that work together in a reasonable way, while the latter leaves me to more DIY it outside of the relatively small base system. (Whether this matters of course depends on what you're building.)