Request meaning of "overload" in a child theme

Hello All,

In the index.php of TwentyTen and also Starkers there is a chunk of code shown below:

<?php
/* Run the loop to output the posts.
/* If you want to overload this in a child theme then include a file
/* called loop-index.php and that will be used instead. */
get_template_part( 'loop', 'index' ); ?>

What does “overload” mean in this context? I have vague ideas but would rather get knowledgeable feedback instead of wondering.

Thanks! -c-