Hi Hugh,
I think Keyboard is really a generic term for anything with piano style keys.
Arranger Keyboards have built in auto accompaniment i.e Styles and yes the Tyros is an Arranger Keyboard
Workstation Keyboards , tend to have the all the voices an arranger does, but without the style or full auto accompaniment
some may have what they call Phrases , which are stripped down styles
and Midi Keyboards just have keys and send out midi data to a computer, sound module etc....
Brian007