An Early adopter is someone who is one of the first to buy the product when introducing a new product. Early adopters are fans of the brand and are willing to buy it for a premium price.
The term early adopter comes from the product lifecycle model. The early adopters are very important for the successful launch of a product. You need people who are willing to buy a product whose utility or success is often not proven yet. For example, consider a Blu-ray player. The early adopters have to wait and see if all films will actually be released on Blu-ray. Therefore, early adopters often become product evangelists of the brand. They are so enthusiastic that they want the product to succeed and to promote it through word of mouth.