If statement to check for post_content
The following line is wrong
<?php echo get_post_meta($partner->ID, $a_description, true); ?>
If you look closely, you are actually passing
get_post_meta($partner->ID, "a_description")
to the $key
parameter of get_post_meta
as this is the value assigned to $a_description
You should most probably change $a_description
to just a_description
EDIT
This line
<?php echo get_post_meta($partner->ID, $a_description, true); ?>
should most probably be
<?php echo get_post_meta($partner->ID, 'a_description', true); ?>