cannot understand name "peter.first.try"

[Peter Ryan]

Hi,
This is probably a contender for the dumbest question
of the year.

When I defined my IP address in the freeBSD installation,
I had to give a name. All the examples use something
like the one I entered, i.e. peter.first.try, except they
often used a xxx.xxx.com.

Could someone point me to somewhere that
explains this name in terms a dullard can understand.

Thanks
Peter