Vdd is an abbreviation for the word “truth”. It is a neologism created in informal communications over the internet and that is part of a specific language called “internetes”. This language is frequently used in online chat programs and social networks, the main ones being: MSN Messenger, Google talk, Facebook, Orkut and Twitter.
Normally, in this type of communication, abbreviations predominate, constituting a form of simplification of writing for faster preparation of the text. In messages exchanged between cell phones (commonly referred to as “torpedo”), the use of abbreviated words is similar.
In the case of Twitter and text messages, there is a limitation on the number of characters for each message sent, so sometimes it is necessary to use abbreviations. In other situations, it's simply out of habit.
Other examples of abbreviations commonly used in instant communications are:
U (you);
kisses (kisses);
all (everything);
today (today);
because (why);
LOL (laughing out loud - laughing loudly)