1.7. What is the FreeBSD-stable concept?

Back when FreeBSD 2.0.5 was released, we decided to branch FreeBSD development into two parts. One branch was named -stable, with the intention that only well-tested bug fixes and small incremental enhancements would be made to it (for Internet Service Providers and other commercial enterprises for whom sudden shifts or experimental features are quite undesirable). The other branch was -current, which essentially has been one unbroken line leading towards 3.0-RELEASE (and beyond) since 2.0 was released. If a little ASCII art would help, this is how it looks:

                  2.0
                   |
                   |
                   |  [2.1-stable]
  *BRANCH*       2.0.5 -> 2.1 -> 2.1.5 -> 2.1.6 -> 2.1.7.1  [2.1-stable ends]
                   |                            (Mar 1997)
                   |
                   |
                   |  [2.2-stable]
  *BRANCH*      2.2.1 -> 2.2.2-RELEASE -> 2.2.5-RELEASE -> ...
                   |       (Mar 1997)      (Oct 1997)
                   |
                   |
                3.0-SNAPs  (started Q1 1997)
                   |
                   |
              3.0.0-RELEASE (Q1 1998)
                   |
                  \|/
                   +
           [future 3.x releases]

The -current branch is slowly progressing towards 3.0 and beyond, whereas the previous 2.1-stable branch was superceded by the release of 2.2.0, the new "stability branch" aka 2.2-stable. 3.0-current will continue to be where the active development takes place, up until the actual release of 3.0. At that point, 3.0 will become yet another branch and 3.1-current will become the next "current branch".