Most of us, these days, prefer to run everything from a GUI. Of course, there are plenty of times when we need to use a terminal. That can be a problem for Emacs users on OS X because there is no way to choose a terminal key for 【Meta】 from Emacs itself. This means that by default you must use 【Esc】 for 【Meta】, which I find clumsy.
Fortunately, Terminal.app has a preference that allows the 【⌥ Opt】 key to be mapped to 【Meta】. That works out well for me because I use 【⌥ Opt】 for 【Meta】 when running Emacs in the GUI.
Lots of people like to use 【⌘ Cmd】 for 【Meta】 though. What can they do? If you’re an OS X user who prefers to map 【⌘ Cmd】 to the【Meta】 key, this post and its comments on the Emacs subreddit has some suggestions. It also explains how to set the Terminal.app preference that I mentioned above. If you’re using Linux, there are also some suggestions to help you with that too.