A second-level domain is "yahoo"
"www" is a gateway name to the network named yahoo : either a server or network node I presume.
I wonder if many ppl mistaken the top-level as 2nd? > http://answers.yahoo.com/question/index?qid=20060618110148AAXC7dV
So, would you like to buy a top-level domain; ".beer" or a second-level domain; "beer.com"