Check if a variable is empty

Programmer Question

I have some user-submitted variables that I want to display in a different part of my site like this:

<div class="pre_box">Term: </div>
<div class="entry"><?php $key='term'; echo get_post_meta($post->ID, $key, true); ?></div>

Occasionally, these variables might be empty in which case I don't want to display the label for the empty variable. In the example above I would want to hide the <div class="pre_box">Term: </div> part. Is there some simple way to check if a php variable like the one above is empty and prevent the label from being displayed?

Update, here is the code using !empty

<?php $key='term' ?>
<?php if( !empty( $key ) ): ?> 
<div class="pre_box">Term: </div>
<div class="entry">
<?php echo get_post_meta($post->ID, $key, true); ?>
</div> 
<?php endif; ?>

However, this still displays the content no matter what. I think the problem might be in the way I am defining the $key variable. Im trying to pull data from a custom field set in a wordpress post - thats what the $post->ID business is all about.

Find the answer here