Magento 2 knockout template rendering via getTemplate

I have been checking out M2’s frontend structure and I stumbled in some knockoutjs’s template binding, for example in Magento/Checkout/view/frontend/web/template/shipping-address/form.html(this file render the add new address popup form in Shipping page of checkout), we got:

<form class="form form-shipping-address" id="co-shipping-form" data-bind="attr: {'data-hasrequired': $t('* Required Fields')}">
<!-- ko foreach: getRegion('before-fields') -->
<!-- ko template: getTemplate() --><!-- /ko -->
<!--/ko-->
<div id="shipping-new-address-form" class="fieldset address">
    <!-- ko foreach: getRegion('additional-fieldsets') -->
    <!-- ko template: getTemplate() --><!-- /ko -->
    <!--/ko-->
    <!-- ko if: (isCustomerLoggedIn) -->
    <div class="field choice" data-bind="visible: !isFormInline">
        <input type="checkbox" class="checkbox" id="shipping-save-in-address-book" data-bind="checked: saveInAddressBook" />
        <label class="label" for="shipping-save-in-address-book">
            <span data-bind="i18n: 'Save in address book'"></span>
        </label>
    </div>
    <!-- /ko -->
</div>

I understand the checkbox part, but not the <!-- ko template: getTemplate() --><!-- /ko -->. I tried deleting one of those and the popup is empty. What is getTemplate() exactly and where can I find the piece of code that it references to?