Someone over at the BSD subreddit expressed ignorance of what this FreeBSD thing is. I typed up a quick explanation. The following is quoted from that:
FreeBSD is one of several modern, direct descendants of the original 1970s BSD Unix — the university offshoot of the (even more original) 1969 Bell Labs Unix. FreeBSD, NetBSD, and OpenBSD are pretty much universally recognized as the “big three” BSD Unix systems now available. They are, in many ways, more Unixy than the commercial UNIX systems many IT pros think of when they hear the term “Unix”.
Many people compare FreeBSD to Linux (I’m pretty sure you’ve heard of Linux), which makes a certain amount of sense since the user experience can be very, very similar to most Linux distributions. FreeBSD has more of a reputation for stability, security, poor software support, and poor hardware support than Linux, though, and many consider it to be a better server platform than the majority of Linux distributions, and a worse desktop platform than at least some Linux distributions. In my experience, the poor hardware support reputation is mostly undeserved, and the poor software support reputation is pretty much entirely undeserved, but FreeBSD suffers from less effective marketing than Linux-based systems due to a comparative lack of religious fervor (relative to the Ubuntu and Gentoo distributions of Linux, for example).
Part of the reason for that less effective marketing is surely the zealousness of GPL advocacy, thanks in part to the efforts of the FSF and GNU project; the Linux kernel and most of the core userland stuff in most Linux distributions is all distributed under the terms of the GPL. By contrast, the BSD Unix systems have BSD licensed kernels and most of the base system’s core userland stuff for these OSes is similarly licensed, and copyfree advocacy is notably less common, voluble, and strident at this time.