What is the difference between Shared and Reseller Hosting?
Shared web hosting service refers to a web hosting service where many websites reside on one web server connected to the Internet. This is generally the most economical option for hosting, as the overall cost of server maintenance is amortized over many customers. (Wikipedia)
Hence the reseller web hosting service refers to a web hosting service in which owner can resell his resources (disk space, bandwidth, mysql servers etc) whit his own customers acting like a shared hosting company. He do not need to buy a server but instead he buy resources on a hosting server to sell to his own customers.