How to use multiple query with same meta key

I use these codes to print custom field query.
My custom field key is out_wiki

    <?php if( get_post_meta($post->ID, "out_wiki", true) ): ?>

        <div class="outlink">
            <a href="http://en.wikipedia.org/w/index.php?search=<?php echo get_post_meta($post->ID, "out_wiki", true); ?>" target="_blank">
                <img src="https://www.wikipedia.com/favicon.ico" title="Wikipedia title">
            </a>
        </div>

    <?php endif; ?>

I want to store multiple values in same custom field key and print them at once. How can I do that?

to store multiple values in same custom field key and print them at
once

If you want to store it as site option, you can use update_option() :

http://codex.wordpress.org/Function_Reference/update_option

Example 1:

// some array to store:
$items=array('yellow','orange','green');

// save the array
update_option('myitems',$items);

// get the array 
$items=get_option('myitems');

// print the array
echo "<ul>";
foreach($items as $item){
    echo "<li>".$item."</li>";
}
echo "</ul>";

If you want to store it as post meta (i.e. for each post), you can use update_post_meta()

http://codex.wordpress.org/Function_Reference/update_post_meta

Example 2:

// some array to store:
$items=array('yellow','orange','green');

// save the array
update_post_meta($post_id,'myitems',$items);

// get the array
$items = get_post_meta($post_id,'myitems',true);

// print the array
echo "<ul>";
foreach($items as $item){
    echo "<li>".$item."</li>";
}
echo "</ul>";

Example 3:

If you want to add the custom fields (same meta key) and values from the backend like this:

you can retreieve the values like this:

// get the array for current post
$items = get_post_meta($post->ID,'myitems'); // we skip the true part here

// print the array
echo "<ul>";
foreach($items as $item){
    echo "<li>".$item."</li>";
}
echo "</ul>";