Reseller hosting is where a Web host buys a bulk plan from the reseller hosting company, and then subdivides that plan into smaller pieces to on-sell or "resell" to individual users.
The reseller host provides large scale hosting packages where, for a fixed cost, substantial packages of space and bandwidth are made available, together with the ability to host bulk domain names. The individual Web host can then concentrate on providing packages and plans to attract customers, without having to own, manage and maintain their own server.