Just to help you realize how easy it is to answer your own questions I just typed in "What is an Arpeggiator" on Google and here you go:

"...In its simplest form, the Arpeggiator takes a series of notes and plays them one after the other up and down a scale, arpeggio fashion, enabling you to create all sort of moving patterns..."

NOt that I didn't know the answer but this just shows you!!!

So go and Google. I'll be around if you need any more help but I'm pretty sure you'll find what you need.

-ED-