When a form containing <input type="text" name="foo" value="bar"> is submitted, $_POST['foo'] === 'bar' in PHP. (And it works similarly for other server-side programming languages.)
<input type="text" name="foo[bar][]" value="yaw" />
$_POST['foo'][0] === "yaw";
When a form containing <input type="text" name="foo" value="bar"> is submitted, $_POST['foo'] === 'bar' in PHP. (And it works similarly for other server-side programming languages.)