[rfc] what is 'merge tracking' means?

[Alexander Belchenko]

My friend ask me recently is bzr has 'merge tracking'? He use svn and
this term appear from their roadmap
(http://subversion.tigris.org/roadmap.html). I say that bzr is
decentralised version control system, so with merge is all right (only
cherrypicking is not implemented). But my friend cannot describe in
simple words what is 'merge tracking', so I'd like to hear from our wise
men what this term should means and is bzr has this thing?

--
Alexander