The biggest difference is that explode() takes in parameters a delimiter to split by, while split() takes a regular expression. This means that explode() runs faster. And even more, the PHP documentation says that preg_split() is faster than split(), so really there isn’t much of a reason to use split() at all.
split() is not an alias of explode() while join() is an alias of implode().
split() function has been DEPRECATED as of PHP 5.3.0. Relying on this feature is highly discouraged.