A business card site is your business card on the web. The main purpose of the site is to acquaint the visitor with information about your company or person.
Typically, such a resource has from two to four pages. This is the main about us, contacts, and reviews.
These kinds of resources are necessary for a small company or a person who provides their services alone. As you already understood, there will be a minimum of information, but the site visitor can easily understand what you are doing and what you are offering.
An important point, a business card site can be easily promoted in search engines, social networks, and also conduct contextual advertising.