So I just purchased a pedal which says consumes "9 - 18V DC"

I have a power supply which accepts 9V pedals. So what exactly does 9-18V DC mean? Will I be able to connect it to my 9V power supply or do I need a power supply that can handle 18V?
It means what it says, it will work with any voltage from 9 to 18v dc.
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
Great! I was just confused if the pedal had some sort of irregular consumption, that it varied from 9-18.

Thanks for the reply!
If its a dirt pedal you might find it has higher headroom when using 18v but, yeah, as has already been explained, it just means you can use an adaptor rated either 9v or 18v and everything inbetween