What is the significance of 3DD in the movie title Piranha 3DD. Is this the lack of new title or any other meaning inside it. Is there any official word on it?
It's a bit of a play on words/abbreviations. The first part, 3D, was for the intention for the movie to be viewed in 3D. The second part, DD (pronounced Double Dee) is a reference to the bra size that some women wear. This is because there are a lot of scantly clad women in the movie, it happening in the water and women wearing bathing suits and all.
Also, the second D is also an indicaiton that it's the second movie. The first movie was called "Pirahana 3D", adding the second D alludes to it being a sequel.