Anonymity of trunk and merges

[Sankaranarayanan K V]

Hi,

(1) How do I refer to the trunk in commands like 

  cvs update -j <branch>

  cvs diff -r <branch>

where branch can be either a proper branch or the trunk itself.

(2) What exactly does HEAD mean?
    Is it the head revision of the trunk or of the sand box branch?

Regards
Sankar