When coding a WordPress theme you’re obviously going to need to link scripts to your theme files. If you were going to link directly a file it would look something like this:
Luckily there is a quicker way to link directly to these files. The following PHP snippet links directly to the root of your theme:
<?php bloginfo('template_directory'); ?>
So to link to the same example file as above you would do this:
<script src='<?php bloginfo('template_directory'); ?>/js/slider.js'></script>
This is obviously easier, less code, and if you move your WordPress install or change the theme name the link will still be correct.