OBB= onboard booking. DCL currently offers 10% off the pretax cruise fare if you book a future cruise while onboard. Up until recently, they also would give us onboard credits for our onboard charging account for that future cruise but that was discontinued in late 2019.
_GT is a special booking offer which there are 3 types:
IGT -guarantees any inside cabin
OGT- guarantees any oceanview cabin (window)
VGT -guarantees any veranda cabin
These offers have a lot of restrictions that would not apply to a regular reservation:
1. Must pay in full at time of booking
2. No changing cabins
3. No name changes
4. No cancellations
5. No refunds
Probably some others as well but this is what I could remember off the top of my head. It's pretty much, "you get what you get & don't get upset".
If you're not picky about cabin location it's a great way to save $.
This is very different from a GTY reservation which is a regular reservation but the category you want is almost sold out so they might list it as something like Cat. 4D GTY which means you're still booking a specific category but you don't know which cabin you'll get exactly. You might get a cabin in a better category but you definitely won't get one in a lower category.
With GTY cabins, you still retain the option to cancel, change categories, change names, etc.
