loadto pick up any changes you made to a file while the program is running.
autoloadto speed up the initialization of your library by lazily loading the modules.
requirewhen you want to use external gems.
require_relativefor local files relative to the current working directory.
Huh, I could have sworn that
autoload was frowned upon and possibly even deprecated. (Something I recall Matz mentioning long ago.) Anyway, this is a good summary!