DDE stands for Disney Dining Experience. It is a card available to Florida Residents and Annual Passholders that gives a 20% discount on sit down meals at participating restaurants, and 1/2 price addmission to Pleasure Island. The card costs $75 for Fl residents, $50 for annual/seasonal passholders. The break even point for AP holders is $250... if you spend more than $250 on sit down dining at participating restaurants in a year, you should consider it.
If you google - DDE Disney - it will take you to the allearsnet page that lists all the participating restaurants.
--heather