When you say flat head screws, do you mean flat head screws:



Those are all flat head screws. When the screw has been screwed all the way in, it does not protrude above the mounting surface. It leaves a FLAT surface. Actually, I find those pretty nice, but they require countersinking for the best appearance.

There is no such thing as a flat head or flat screwdriver, as no screwdriver can run all of those in.

or do you mean slotted head screws:



Those are slotted head screws. No matter what kind of head shape it has, it requires a slotted screwdriver to drive it in.

For a similar case, see many many comments regarding baluns, adaptors, and converters, which are ignorantly all referred to as baluns. And ignorantly pronounced as bay-luns.