The traditional key with one set of cuts on the bitting.
A key with several sets of cuts, thus giving them multiple bitting surfaces. Common in high security locks that have auxilliary locking mechanisms, such as a sidebar.
A key with duplicate cuts but only one actual bitting surface, allowing the key to be functional when inserted in any orientation.
A key that has four bittings, giving it a star shaped tip. May not actually use all four, like a convenience key.
A key that has an electronic transponder in the bow of the key that transmits a code to a receiver in the lock. Most commonly seen in automotive keys. Requires specialized equipment to copy.
A special type of automotive key that can be used by a valet driver. Typically, a valet key can operate the doors and ignition of a car, but can't open the glove compartment or trunk.
A key that has had no bitting cuts applied to it. "Blanks" are a common locksmithing item used for duplicating keys, impressioning, and creating bump keys.