The stuff that’s included in the system after a standard install, before you install any additional stuff. It’s all in one repository and it’s maintained by the FreeBSD project. Stuff like the kernel, libc, utils, dtrace, compilers needed to build base, ... Basically everything that’s needed for a usable system. It’s updated all together through binary patches, not separately through packages like on Linux. When you want something more, you either compile it from source using Makefiles stored in a repository called “ports” (the Makefiles download the tarballs with source code, verify their checksums, build them etc), or you install pre-built packages using the pkg package manager.

The FreeBSD project tends to like to slim the base system down. E.g. some years ago they removed Perl from the base system. So out-of-the-box the only scripting language that’s available is shell. In contrast, OpenBSD has more stuff in its base system and on the subject of Perl they doubled down on it (their package manager e.g. is written in Perl). It’s also visible, when you download the base system repos for each of them and run tokei to find out the numbers of LOC. (I don’t remember the numbers off the top of my head.) That said, FreeBSD still includes a full LLVM toolchain due to the rule “base builds base”, and LLVM is... a lot. It’s the biggest source of bloat in my jails to be honest. I keep meaning to find out if I can remove it from them.

The kernel, libc (they tie libc to the kernel unlike Linux), and a standard suite of programs.