It's called a "spanner".
Spanner
Sometimes also known as “snake eyes” and “notched.” Though the diagram shows two holes in the top of the screw, these sometimes also look like a screw with two notches cut into the edge on opposing sides of the screw. A commonly used screw head to avoid tampering, used in everything from electronics to bathroom stall doors in public restrooms!
Here's a good List of Screw Types.
