Wood screws have large threads for use in wood.
Flat heads are countersunk (cone shaped under the head) with a flat top. Phillips drive is x-shaped for installation with a Phillips screw driver.
A low carbon steel for general use. Zinc plated for moderate corrosion resistance.
Round heads are domed and look like half of a sphere. Phillips drive is x-shaped for installation with a Phillips screw driver.
Screws with large threads for use in sheet metal sometimes also used in plastic, fiberglass or wood.
Screws for wood to wood fastening applications such as decks, docks and ledgers, etc.