Emacs is a customizable text editor that originated from the TECO editor. It has a long history from early versions like Multics Emacs and GNU Emacs 13.0. Emacs has powerful editing commands, window operations, and help systems. It can be customized through user init files, built-in customization, and many third party extensions. Emacs Lisp allows for extensive customization and extension of Emacs through scripting.