They call it a dilogy or duology.
pentalogy
tetralogy
A trilogy
A trilogy.
Yes there are 2- 3 books in the series
There are currently three books in series 2
In the first series there are Seven books, however there are 2 or more books in the second series that I know of. The first two are Phoenix and Lion
There will be 10 Books in Series #1. There will be a Series #2 called Vespers Rising it will be out April 2011.
I only know of 2 books
You could have googled this, but from what i have found there are 2 series. In the first there are 30 books, and in the second there are 19.
2 and maybe more
2