What does the theme name in parameter do?

I’m using Boilerplate to build out a theme and I see the theme name used as a parameter in there and in twenty eleven. I was wondering what that does and if I can change or remove it. Here are a couple examples of where I’ve seen this:

<nav id="nav-above" class="navigation">
<?php previous_post_link( '%link', '' . _x( '&larr;', 'Previous post link', 'boilerplate' ) . ' %title' ); ?>
<?php next_post_link( '%link', '%title ' . _x( '&rarr;', 'Next post link', 'boilerplate' ) . '' ); ?>
</nav><!-- #nav-above -->

<nav id="nav-single">
<h3 class="assistive-text"><?php _e( 'Post navigation', 'twentyeleven' ); ?></h3>
<span class="nav-previous"><?php previous_post_link( '%link', __( '<span class="meta-nav">&larr;</span> Previous', 'twentyeleven' ) ); ?></span>
<span class="nav-next"><?php next_post_link( '%link', __( 'Next <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?></span>
</nav><!-- #nav-single -->

Thanks