The “global” keymap is the most important keymap because it is always in effect. The global keymap defines keys for Fundamental mode; most of these definitions are common to most or all major modes. Each major or minor mode can have its own keymap which overrides the global definitions of some keys.
Commands to rebind keys, such as ‘M-x global-set-key’, work by storing the new binding in the proper place in the global map. To view the current key bindings, use the ‘C-h b’ command.