Zsh is a UNIX command interpreter (shell) which of the standard shells
most resembles the Korn shell (ksh), although it is not completely
compatible. It includes enhancements of many types, notably in the
command-line editor, options for customising its behaviour, filename
globbing, features to make C-shell (csh) users feel more at home and
extra features drawn from tcsh (another `custom’ shell).
If you want to use zsh completion system, you should type the following
$ autoload -U compinstall
See also zshcompsys(1) manpage.