Loop template files are used to format the loop based on what type of page you are visiting.
You can have loop templates for different loops. For example: loop-archive.php or loop-category.php which represent different loops for archives and categories, respectively.
You can call a loop from inside one of your page templates like this:
<?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', 'category' );
?>
Using this method will call the file loop-category.php and run the content within in it. Inside loop-category.php you might have code to format the loop just for category pages.
Template Hierarchy: Category Templates, Tag Templates, Taxonomy Templates, Page Templates, Post Type Templates, Author Templates, Date Templates, Search Templates, 404 Templates, Attachment Templates, Loop Templates