UFS stands for UNIX file system, which was originally developed from the first versions of UNIX at AT&T. The file system reached its current status in the 4.x BSD distributions. It it currently used in FreeBSD, NetBSD as well as OpenBSD. Linux support is availible, but is not standard.
FreeBSD versions 5.0 introduced UFS2, which allows soft updates, a more efficent method of writing file system meta data, as well as support for volumes over 1TB in size.