Difference Between parse_variables_row and parse_variables

gistfile1.txt

ee()->TMPL->parse_variables_row(array(
	'var_1' => 1,
	'var_2' => 2,
	'var_3' => 3
));

ee()->TMPL->parse_variables(array(
	array(
		'var_1' => 1,
		'var_2' => 2,
		'var_3' => 3
	),
	array(
		'var_1' => 4,
		'var_2' => 5,
		'var_3' => 6
	),
	array(
		'var_1' => 7,
		'var_2' => 8,
		'var_3' => 9
	),
));