That qualifies for funniest answer.
Now some more ...
90+10 refers to how Disney on-site guests can book dining and activity reservations.
90 days out from your check-in date, you can book for 10 days worth of reservations on one phone call.
Off-site guests also call 90 days out ... but from the date they want their reservation on. And they have to call every 90th day out from each day that they want a reservation. So if they want 5 ADRs for their trip for 5 different days, they need to make 5 separate calls. If an on-site guest wanted the same, they can do it in one phone call.
The "+10" is a perk for staying on-site.