premsingh is correct. The sub-domain is a precursor to your base domain. While I can't speak in-depth of the Hubpages su-domain policy, but the way it works sub.domain.ext is correct. So, you might have one like biz said www.buycars.com and you want to try and get traffic geared more toward buying toyota cars. Most SEO people will tell you it's best to have www.buycars.com and www.buytoyotacars.com or www.buytoyotas.com or some such thing. However, to save money many will instead keep www.buycars.com and not buy a new domain just do www.toyota.buycars.com. I've seen it work and help with searches, however, I haven't seen it help as much as I wish it would.