In a traditional climbing system,
the climbing line is tied to a connector
(usually a locking snap), and a long tail is
left in the knot. This tail is then used to tie
the climbing hitch on the fall, or standing
part, of the climbing line.
In the split-tail system, the climbing line
is attached to the connector using an appropriate
endline knot or an eyesplice. The climbing hitch is tied using a short, separate piece of rope called a split-tail. The split-tail may have only one eye--the eye is attached to a carabiner and the tail is used to tie a climbing hitch to the fall of the climbing line. Or the split tail may have two eyes--the split tail is used to tie a climbing hitch and both eyes are attached to a carabiner.
Adapted from pages 2-3 of this article:
http://www.treebuzz.com/pdf/climbing_hitches.pdf
See the sections titled 'Open Hitches' and 'Closed Hitches'.