What is the Middle East, Anyway?

Here's one view:

Credit: map-zone

And another:

Credit: Bryn Mawr Library

Or this:

Credit: University of Notre Dame

The folks at mideastinfo include 21 countries in the middle east:

1. Algeria
2. Bahrain
3. Egypt
4. Iran
5. Iraq
6. Israel
7. Jordan
8. Kuwait
9. Lebanon
10. Libya
11. Morocco
12. Oman
13. Palestine
14. Qatar
15. Saudi Arabia
16. Sudan
17. Syria
18. Tunisia
19. Turkey
20. United Arab Emirates
21. Yemen

But the so-called "traditional" Middle East differs (excluding northern Africa), as does the "greater" Middle East (which includes Afghanistan, Cyprus, and others), as per wikipedia.

Does one define the so-called "middle east" by:

• Location on a map? 
• Predominant religion? 
• Language?
• Oil?
• Political alliances?
• History?
• Desert?
• Populations' phenotype?