A modal is a dialog window which can be displayed over the current page.
<!-- Clicking the button will open the modal window -->
<button type="button" class="btn btn-success btn-lg" data-toggle="modal" data-target="#theModal">Open The Modal</button>
<!-- The Modal -->
<div id="theModal" class="modal fade" role="dialog">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal">×</button>
<h4 class="modal-title">Text For The Modal Header</h4>
</div>
<div class="modal-body">
<p>Text for The Modal Body.</p>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>