page/elements/footer is the content that goes inside this part of the page:
<div class="elgg-page-footer">
<div class="elgg-inner">
<!-- page/elements/footer goes here -->
</div>
</div>It's content is visible to end users and usually where you would put a sitemap or other secondary global navigation, copyright info, powered by elgg, etc.
page/elements/foot is inserted just before the ending </body> tag and is mostly meant as a place to insert scripts that don't already work with elgg_register_js(array('location' => 'footer')); or elgg_require_js('amd/module');. In other words, you should never override this view and probably don't need to extend it either. Just use the elgg_*_js functions instead