It it's simplest definition, domaining is the monetising of domain names.

Monetisation is generally acheived through buying domain names and selling them on for a higher price or earning revenue from advertising placed on the domains' websites. Although more complex scenarios exist, a typical domainer buys domains, lists them with a domain parking provider, and attempts to sell them through auction sites or direct enquiries.

Domain names can be acquired by:

Profits are generally made through one or more of:

Other monetisation possibilities exist such as:

As in any business, profits are not always made. Domain names require yearly renewal fees to be paid so losses will be made on any domains that are not sold and earn less in advertising revenue than they cost in renewal fees. Many domain portfolios are run at losses on advertising and fees but the domainer still hopes to profit from domain sales, which are generally several multiples higher than the purchase price and renewal fees.