Terminology

Command line argument: A string from the console window, given to the running program by the shell. A command line argument can be a command line option or a positional argument.
Command line option: A string, prepended by a dash '-' or a double dash '--' which represents the name of a program option.
Positional argument: Also referenced as value. A command line argument whose interpretation depends on its position on the command line.
Switch option: An option without any arguemnt. The value type of the switch is a boolean. True when it appears at least once on the command line.
Single argument option: Also referenced as argument option. An option whose value depends on the following argument on the command line. The value type is a string.
Multi argument option: An option which accepts more than one arguments. The value type is an array of strings.
Program scope option: A program scope option is an option available in the program and its subcommand.
Subcommand scope option: A subcommand scope option is only available in a given subcommand.