This aim of this note is to provide the shortest and simplest explanation of the concepts of trunk and HEAD in a Version Control System like CVS and Subversion (SVN.)
Like in botany, trunk is a tree’s central superstructure. All branches come out of the trunk:
Main development is performed in the trunk. Releases are branched for bug fixes and maintenance releases.
In the next diagram, the tip of the arrows for trunk and a branches are HEADs. Each branch and trunk have a HEAD.