Thad is probably one of the few names that you've heard before. Curiously, Thad could be a short name for Thaddeus which was mentioned in the Bible. It could be a name of a movement of missionary people that preaches and spreads the word of Christianity. Thaddeus means a courageous heart. Thad is a somewhat popular first name for men but an uncommon surname or last name for all people.
Then there is also a different definition of its name. Thad, according to the urband dictionary, is a unique and musical creature with lots of emotional and mental baggage. Will go far, but will do it very loud and obnoxiously. A great creature to hang out with, makes the party lite and fun, but doesn't mind being a real doucher when he deems it necessary.