Wood screws have large threads for use in wood.
Note: These screws are not compatible with Phillips drivers/bits.
Flat heads are countersunk (cone shaped under the head) with a flat top. Frearson drive is x-shaped, similar to (but not compatible with) Phillips.
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.