A portfolio website provides an online presence and an overview of your company. Potential customers can go to this site to find out what work you have done and how they can contact you.
This site is designed primarily to generate leads through an online presence. SEO and targeted marketing techniques play a huge role in bringing in new customers. Sales take place, however, offline.
This popular type of website is a site that sells products or services online and collect payments. If a website has a cart function, then it falls under the sales website category.
Utility websites function more like a tool than a standard website. These sites don't necessarily generate sales and leads. This includes blogging and software like services.