:) Hi Iwan,
Simple explaination: A reseller is some one (B) who purchases web hosting space and bandwidth from a parent hosting company(A) for a bulk discounted price, then brakes it up into smaller accounts and sells that space and bandwidth under their company name at an increased price to their customers, thus allowing them to make a profit. The parent hosting company(A) remains anonymous so that it appears that (B) is the sole provider of that space and bandwidth.

I hope this helps :)