I have a Skagit line that I use on one of my rods. On the other I use an Airflow Delta Multi Tip. What catagory does the Airflo belong in?
Your Delta is a shorthead spey.
I would roughly group them something like this:
Shooting heads (skagits & scandi)
Shorthead spey lines (Delta, WC, SA Spey Shorthead, ect)
Mid-length spey lines (MidSpey, Delta Long, SA Spey Classic, ect)
Long bellies (Nextcast 95, GrandSpey)
Double Tapers (CND, SA Salmon DT's)
Some lines cross a couple head length classes as they get heavier (CND, XLT, Carron Jetstream)
The above are a just few examples and like many things in the spey tackle world there are some overlaps and exceptions.