In brief...
One of the veteran BSDs, widely reputed to be a rock-solid, no-nonsense operating system. BSD licensing is simple (between two and four clauses and not a whiff of any copyleft conditions). Hardware support isn’t quite up to Linux standards, but is improving.
For various reasons, your casual Linux user, plucked from their penguin paradise and deposited in BSDtown, may experience disorientation, confusion and feelings of impending doom. This is especially true, we discovered, if one chooses one of the traditional BSDs, such as FreeBSD.
The BSD family are not all based around a common kernel, so strictly speaking they are all distinct operating systems. That said, many are derivatives of ‘The BSDs’ (the Free-, Open-, Net-BSD triumvirate), so we can refer to PC-BSD (see p21) as a distro…