A domainer is someone that does buiness in the domain name industry. They generally own hundreds or thousands of domains, but they may own as little as one domain worth millions. They may be a speculative investors like Frank Schilling that buy domains to sell in the future when they are worth more, an income investor like Kevin Ham who parks domains with ads, or a developer that will buy domain names and then develop some kind of site on each domain.
"The domainer used his life savings to buy one domain name that cost $320,000. That sounds crazy but the domain earns $150,000 a year from parking ads".
"Some domainers buy and sell domain names like baseball cards and try to get some profit with each transaction."
"When I realized I owned 50 domains I started feeling like a real domainer".