A loose affiliation of people and organizations spread across dozens of countries. They have several traits in common:
1. They are Muslim
2. They wish to use violence to institute a society ruled by their belief system, which is a mix of religious and political
3. Most of them are Arab
Since there are many people who fit this set of traits who are we are not fighting against, and because these people are not confined to a particular country with a government, fighting against them is uniquely difficult. It leads to many mistakes, which are then exploited by our enemies.
Well said, sir. Rep points for you.