There are currently three active/semi-active branches in the FreeBSD CVS Repository (the RELENG_2 branch is probably only changed twice a year, which is why there are only three active branches of development):
RELENG_2_2 AKA 2.2-STABLE
RELENG_3 AKA 3.X-STABLE
RELENG_4 AKA 4-STABLE
HEAD AKA -CURRENT AKA 5.0-CURRENT
HEAD is not an actual branch tag, like the other two; it is simply a symbolic constant for ``the current, non-branched development stream'' which we simply refer to as ``-CURRENT''.
Right now, ``-CURRENT'' is the 5.0 development stream and the 4-STABLE branch, RELENG_4, forked off from ``-CURRENT'' in Mar 2000.
The 2.2-STABLE branch, RELENG_2_2, departed -CURRENT in November 1996, and has pretty much been retired.