Perhaps "alias" is an incorrect term...it certainly does have some negative connotations!
It's simply a term I use to imply an alternative "name" for someone. "Name," in this case being an email "name," actually an email address. Most (he says, without doing much actual research!) Internet service providers (your cable, phone company or Earthlink, AOL, etc.) and certainly Gmail or MobileMe and their ilk provide you with the opportunity to have multiple email addresses. They will all get forwarded to your primary address.
As an aside, you don't even need to have more than one 'account' set up in most email apps. I have an account with Comcast, since they 'provide' my Internet connection. But I found it simpler and less troublesome, to just assign my .Mac address at the Comcast email preferences. Thus, I have only one account in Mail, but anything sent to my Comcast address(s) still gets to me because it is forwarded to the .Mac account in micro-seconds. This also makes it easier to check my email while traveling, I only have to surf to my .Mac account and it has all messages from where ever they may have been sent.
"Any fool can make something more complicated, it takes genius to make a complicated thing easier." Paraphrased statement of A. Einstein
