Esc *is* Meta, but not like Alt #2
Description
🤔 Why Though? The "Meta" key comes from ancient Lisp machines that had actual Meta keys. Your keyboard doesn't have one, so we use Alt. Or Escape. Yes, pressing Escape and then the key also works. No, I don't know anyone who does it that way. Yes, it's there if you're using Emacs on your phone for some reason.
Many early text terminals (I'm talking 80's here) had a Control/Ctrl key which mapped keys in the range of 0x40-0x5F (@, A-Z, [, \, ], ^, _) to the ASCII control characters 0x00-0x1F (NUL-US, see the chart for the meaning; ESC is 0x1B). These terminals did not have a Meta, an Alt, or any other "modifier" keys other than Shift. Since Emacs used Meta so frequently, it was mapped to Esc, but not as a modifier (pressed concurrently) since Esc was an actual character like x is a character. So if you have an Alt or Cmd key, you may press it and the other character to get the Meta modifier (e.g., Alt+x is M-x to Emacs). Without an Alt/Cmd key, press Esc and release it, and then press the following character: Esc x is M-x, Esc Control+s is M-C-s.
In places where the desktop environment grabs the Alt/Cmd key for its own purposes (e.g., Alt+Space under Gnome is captured before it is delivered to the application like Emacs and pops up a workspace menu, but Esc Space is delivered as M-SPC to Emacs.
One final note: All of the "modifier" type keys can be simulated with C-x @ followed by a letter representing the modifier (Press C-x @ ? to see the list).