I've only ever used PG & VG but I came across AG (aqueous glycerine) on the Totally Wicked website yesterday.
It says its watered down glycerine, a less thick version of VG I think.
Can AG be used instead of PG?
yep, just a thinned gown vg, using lab de ionised water to thin down vg, used so you dont have to have extra pg in juice that needs to be a bit thinner
It is glycerine with purified water added. If you add 10% purified water then your vg becomes about as runny as 50pg/50vg. I use pure vg with 5% water as my base for all my diy stuff (consistency is same as 30pg/70vg).