What is the difference between a turn signal swith and a turn signal flasher on a 2004 Ford Taurus?

The switch is the turn-signal 'stalk' coming off the steering column. That's where the 2 different switches are located, activated by the movement of the stalk.

The flasher is what generates the blinking action - interrupts the electric current. In years gone by, the flasher unit was a silver can, about the size the old film canisters were, and often mounted directly on the fuseblock...

For reference to more current configurations, the 1996+ Taurus / Sable flashers are a blue rectangular box, and mounted away from the fuseblock (See "Related Questions" below for more)