Why callback function is not working in wp_head hook?

I found answer i do not need to return value, i must echo it.
So my function should look like:

function custom_description(){   
    echo  '<meta name="description" content="cococo" />';
 }

This works !

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)