Reseller Web Hosting is the practice of reselling web hosting space to sub-clients. As a Reseller, you purchase large blocks of disk space, bandwidth, and server resources and then divide it up into individual packages to resell to other clients for a recurring fee (i.e. monthly, quarterly, annually, etc.).
As a Reseller, you're able to purchase these larger blocks of disk space and bandwidth starting at around $20 a month. Therefore it only takes about five or so clients at $5 a month to cover your expenses.
With returns this large, it doesn't take long to start developing a very profitable business.
Being a reseller gives you the ability to own and operate the business without the headache of having to own, lease, or even managed servers.
When you purchase your Reseller Web Hosting package from a reputable company, they handle all of the server updates/upgrades, security hardening, and the good ones (like Encrypted Hosting ;)) , also back up your customer's data. Therefore your only job it to resell space/bandwidth/server space to your customers, handle their billing, and provide level 1 technical support.
With server management, security, and leasing costs factored into your monthly reseller hosting fee, the benefits to being a reseller are tremendous. As long as you're working with a reputable company, you stand the chance to make astronomical returns, with not a ton of day-to-day overhead tasks.