The short answer: the HOA covers ongoing upkeep and rules; the CDD repays the roads, water lines, and amenities that were built before you moved in. They are separate charges, and a CDD can add hundreds to thousands of dollars a year on top of HOA dues — sometimes for 20 to 30 years.
HOA — the private association
A homeowners association maintains shared areas, may run amenities, and enforces community standards. Dues are billed by the association (monthly, quarterly, or annually) and it can place a lien for non-payment.
CDD — the government district
A Community Development District is a special-purpose unit of local government that issued bonds to fund infrastructure. Your CDD assessment usually has two parts: a debt-service portion that pays off the bond and eventually ends, and an operations-and-maintenance portion that continues. It appears on your annual property tax bill, not a separate HOA invoice.
Why it matters before you offer
A home can look affordable on the listing and then carry a four-figure CDD line you did not budget for. I confirm both the HOA dues and any CDD assessment before you write an offer, because together they change your real monthly payment. This pairs with insurance as the two costs that most often surprise buyers here.