[thelist] name of function / cascading menu effect

[Bob Meetin]

what is the name of the function, also what is used to create a 
cascading menu system:

1) select vehicle type (car or truck)
2) if car, second menu dynamically lists: audi, jensen, mercury, 
pontiac, volkswagen
3) if select jensen, third menu dynamically changes to list jensen 
healey or jensen interceptor

what is this called?

language? javascript, mootools, jquery, ajax?