This section is from the "Version Control with Subversion" book, by Ben Collins-Sussman, Brian W. Fitzpatrick and C. Michael Pilato. Also available from Amazon: Version Control with Subversion.
There are two important lessons that you should remember from this section. First, Subversion has no internal concept of a branch—it knows only how to make copies. When you copy a directory, the resulting directory is only a “branch” because you attach that meaning to it. You may think of the directory differently, or treat it differently, but to Subversion it's just an ordinary directory that happens to carry some extra historical information.
Second, because of this copy mechanism, Subversion's
branches exist as normal filesystem
directories in the repository. This is different
from other version control systems, where branches are
typically defined by adding
extra-dimensional “labels” to collections of
files. The location of your branch directory doesn't matter
to Subversion. Most teams follow a convention of putting all
branches into a /branches
directory, but
you're free to invent any policy you wish.