What's the technical RFC allowed way to do this?

[Matt]

Hello,
Here's a question to which I've received different answers and I'm 
hoping to be able to get a straight answer.

The domain yadda.com
Am I allowed via RFCs and such to point yadda.com to the yadda website? 
  Or must I point www.yadda.com to the website?

I was under the impression that domain names were not to be used for 
that but rather hostnames were (www.yadda.com).

Can someone clarify?

~ Matt