According to the PHP manual:
Sets the magic_quotes state for GPC (Get/Post/Cookie) operations. When magic_quotes are on, all ‘ (single-quote), ” (double quote), \ (backslash) and NUL’s are escaped with a backslash automatically.
But does this also apply for $_REQUEST variables?
Yes it does since
$_REQUESTis derived from content stored in$_GET,$_POSTand$_COOKIE. However as I am sure you already noticed relying onmagic_quotesin any way is considered bad practice which is why it was ultimately removed as of PHP 5.4.