I'm taking an educated guess here and saying that it's selling a domain name to someone else, but how does the process work exactly?
Reselling generally refers to buying a block of disk space and bandwidth and reselling that to other people needing hosting. It can also refer to any commodity that is purcahsed for resale and domains would be included.
reselling means you buy from someone and sell to someone else. re-sell. for example, you could be a business owner buying from distributors and reselling to end users. in hosting world, you can sign up for a reseller hosting account and sell hosting to indivisual clients