Yes,exactly, big four are four top most or we can say Big4 firm of Chartered Accountant of the world. & those firm names are-KPMG, Delloite, PricewaterhouseCooper(PWC) & Ernyst & Young (E&Y).
This group was once known as the "Big Eight", and was reduced to the "Big Five" by a series of mergers. The Big Five became the Big Four after the near-demise of Arthur Andersen in 2002, following its involvement in the Enron Scandal.
After the Satyam & Global Trust Bank scam I think now we should open a new community- BIG CHOR (Big Thieves) instead of the current Big4. As no one takes as much bribes to hide so enormous size of frauds as BIG CHOR do....