Officially, the name of the magazine is "NF Magazine." We use the term "Nintendo Force" informally, to refer to the group of people who make the magazine (and our supporters, which is why we say "Join the Force!" a lot). We needed something to call ourselves, and someone suggested "the Nintendo Force" while we were working on our first magazine issue – it sounded like a great rallying-cry team name, so we went with it.
We also used it as the theme of the first issue, which is why that one's referred to as "Issue #1: Nintendo Force." The issues after that one have all had different themes and their own individual names – Issue #2 was "A Celebration of Sequels," Issue #3 was "Nintendo at the Movies" and so on.
But yes, the magazine itself is NF Magazine. :) Hope that clears things up!