dot file [Unix] n.
A file that is not visible by default to normal
directory-browsing tools (on Unix, files named with a leading dot
are, by convention, not normally presented in directory
listings). Many programs define one or more dot files in which
startup or configuration information may be optionally recorded;
a user can customize the program's behavior by creating the
appropriate file in the current or home directory. (Therefore,
dot files tend to creep -- with every
nontrivial application program defining at least one, a user's
home directory can be filled with scores of dot files, of course
without the user's really being aware of it.) See also profile (sense 1), rc file.