 <p>It think you mean <a href="http://goose.ycp.edu/~dhovemey/fall2011/cs201/lecture/lecture25.html" rel="nofollow noreferrer"><em>Sentinel nodes</em></a> in a linked lists.</p> <p>Some linked-list implementations put one or two extra nodes at the beginning and ending (or both of them) to implement some algorithms simpler. These nodes don't hold special data as a entry of data-structure. It's an alternative for using<code>NULL</code> as first/last node indicators.</p> <p><img src="https://i.stack.imgur.com/K9CyZ.png" alt="enter image description here"></p> <p>The <code>std::list</code> is supposed to be a list in the standards. It maybe uses <em>sentinel nodes</em> or not.</p>