$PATH—When used as a variable, it contains a list of directories that will be searched for executable files when a user enters a command.
. (period)—Shorthand for the source command, a bash shell built-in command that specially runs or loads the content of the file passed as argument in the current shell. See sourcing. Can also refer to the current directory, which can be requested using the pwd command.
absolute file name—A file name that is complete and starts with the name of the root directory, including all directories up to the current file or directory.
absolute path—The location of a file or directory that starts from the root of the filesystem, and therefore begins with a slash character (/).
access control list—In Linux permissions, ...