Wiktionary
n. (context Internet English) A small web site.
Wikipedia
A minisite is a website by which companies offer information about one specific product or product group. Typically, a minisite is enhanced by various multimedia content, such as an animated, narrated introduction, and accompanied by a visual scheme which complements the product well.
For example, a soft drink company might have a minisite with bright colors and a carbonated bubble motif. This offers a more immersive experience for the visitor, in comparison to a traditional corporate website, which is usually presented in a classic professional layout describing the company's statistics and range of operations, and products' technical details.
A minisite may also refer to a single-page website through which the operator aims to sell one particular product rather than present a company's product portfolio. Unlike traditional websites, minisites usually consist of a single page website that utilizes a direct response marketing approach to sell its single product. Such products are often digital products that can be sold in a number of electronic formats such as PDF eBooks, interactive web videos, software, audio, podcasts, membership subscriptions or an online eCourse. However, it is also not uncommon for a minisite to sell a physical product.
Minisites have existed since the popularization of the World Wide Web in the mid 1990s as direct marketers adapted their offline direct mail campaigns to accommodate for a worldwide audience provided by the Internet.