The CDD fee is basically a bond payoff. A community puts in a swimming pool, etc. The cost is paid for by a long term, say 30 years, by a bond. Each member of the community pays the interest and principal via the CDD. The CDD usually shows up next to your county real estate tax, on your tax bill. Thus you get the opportunity to write it off, as if it were tax, on your federal return.
CDDs are usually associated with planned communities with lots of ammenities.