Bol-Bachan or Bol vachan actually, is a term that is generally used for the intellectual 'gyaan' given by yogis, babas, and such ascetic people, many a time in a sarcastic sense.
However, Rohit Shetty is making a movie called Bol Bachchan, starring Abhishek Bachchan and it's notable that the spelling of the Bachan part goes on to be the same as that in the name of the actor.
Literally, and separately, bol and vachan are two words with the same meaning 'something that is said, or spoken.'