dot file

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.