I used to think there was a department of the military that came up with the official name for conflicts. Someone must have decided to call the conflict from 1914-1918 "The World War", and then decided that the conflict from (take your pick, 1933-1945 or 1939-1945) "The Second World War".
As for the current conflict, there's not really a general consensus on what to call it, as a number of titles have been thrown out. The most predominant one is the "Global War on Terror(ism)". We throw around the words "War on Drugs", "War on Christmas", "War on Cancer", etc to such an extent that the term really has lost its meaning.
Not to mention, the term "terrorism" can be problematic. Certainly, there are a number of terror organizations which the US is currently and rightly engaged in combat with, most notably Al Qaeda. However, lumping everyone on the battlefield as "terrorists" is an oversimplification, as we've found out there's no real monolithic enemy of the US on the battlefield, rather, we face multiple terror and insurgent networks, organized crime groups, and even "accidental guerillas". Many of the terror and insurgency groups in the world today disagree as fiercely with each other as much as they disagree with the West (a la Monty Python and the Life of Brian's Popular Front for the Libeation of Judea).
David Kilcullen, one of the key counterinsurgency advisors to General Petraeus, challenges the notion of a "War on Terror" "The Accidental Guerilla: Fighting Small Was in the Midst of a Big One" and instead, re-frames many of the tensions in the modern world in the context of four main theories, none of which are mutually exclusive, and includes Al Qaeda and other such organizations (takfiri, as he terms them) as the major adversaries of the West. Seriously, you need to read this book, if only for the first 30 pages or so.
1.) A backlash against globalization--a process which has, as an unfortunate byproduct, created many "haves" and "have-nots", and makes the "have-nots" well aware of what the "haves", erm, have. This model assumes that Al Qaeda and other organizations don't seek to prevent globalization, but rather, seek to have globalization operate on their own terms.
2.) Global Islamic Insurgency Model--a process through which, Al Qaeda and other organizations (tafriki) seek to mobilize the 1.2 billion Muslims in the world as an insurgent network against the West. A counter to this would be a stability/counter-insurgency campaign to dissuade the majority of Muslims who don't subscribe to Al Qaeda's views.
3.) A Civil War Within Islam--a movement which seeks first to subjugate and unify the entire Muslim world (using the US as a common, unifying enemy), which would then be organized to take on the West.
4.) Asymetric Warfare--American dominance in military spending and technology (accounting for well over 50% of all global defence spending) has caused anyone who wishes to take on the US to resort to asymeteic insurgent tactics.
Great analysis from one of the world's greatest counterinsurgency experts. I think I went through an entire highlighter in the first 30 pages of this book.