HTML: HTML (Hypertext Markup Language) is a set of instructions to a browser about what information to include in a web page (text, hyperlinks, but also images, sound, and other media). It provides structure and organization for the layout of the page. A hyperlink is an HTML element that redirects the user to another page.
CSS: CSS (Cascading Style Sheets) defines the style and layout of HTML elements (i.e: color, size, typography etc…)
HTML5 and CSS3 are simply the latest revisions to HTML and CSS. They provide new means of embedding media (displaying them directly on the page instead of downloading or redirecting to a separate page), creating simple animations etc… These revisions were instituted by the W3C (World Wide Web consortium), the international Standards organization for the world wide web
– Anna Pinkas