Flat heads are countersunk (cone shaped under the head) with a flat top. Slotted drive has a simple slot for a flat bladed screw driver.
Sidewalk bolts have a wide, low profile head and are often used in hurricane shutter installation. Slotted drive has a simple slot for a flat bladed screw driver.
Screws with machine threads for use with a nut or in a tapped hole.
Screws with an Allen wrench drive.