FreeBSD is an operating system that traces it’s heritage back to the original unix development at AT&T starting in 1970.
The BSD part of the name refers to 'Berkeley Software Distribution' which is also part of it's origin, being mostly a variant of the AT&T unix developed by staff and students at Berkeley University. From there the first 'public' project was called 386BSD reflecting the aim of getting it to run on Intel hardware. While NetBSD forked from 386BSD early on with the aim of supporting as many different hardware architectures as possible, the name FreeBSD was in use later the same year.
While FreeBSD has kept it's focus on a text based system to form a solid base for reliable servers, PC-BSD has focused on a gui desktop version of FreeBSD for the average user.
Don't let the text based focus scare you away, Xorg, gnome, KDE and just about any other open source project will also run happily on a FreeBSD machine. If getting into the technical side of things scares you then PC-BSD can still keep you happy.