An internal stylesheet is where you don't have an external CSS file, but instead place your CSS inside a <style> element, contained inside the HTML head. So the HTML would look like it does in this page (see the internal code). This can be useful in some circumstances(maybe you're working with a content management system where you can't modify the CSS files directly), but it isn't quite as efficient as external stylesheets - in a website, the CSS would need to be repeated across every page, and updated in multiple places if changes were required.