What is an "igniter"?

Replacing the igniter in my 91 SE solved the stalling problem. I'd just like an idea of what that part actually does. Its a little ceramic plate with 4 electrical connections, attached to a metal plate and it slides into the distributor. Anyone know its function?

Gaff
Toronto, Canada

It is essentially an solid state switching device. It receives a grounded pulse from the ECU which causes it to connect the negitive side of the coil to ground. It takes the place of the points we had in older cars.