HTML (the Hypertext Markup Language) and CSS (Cascading Style Sheets) are two of the core technologies for building Web pages. HTML provides the structure of the page, CSS the visual layout, for a variety of devices. Along with graphics and scripting, HTML and CSS are the basis of building Web pages and Web Applications.
HTML websites are old school, but really fast, especially on shared hosting. The average time spent on a web page is 10 seconds -- you don't want to lose half that time loading a page, assuming your customers will wait that long.
HTML is great for small sites of a few pages. Development costs will be higher for larger sites than for comparable CMS-based sites.