B-School = Business School
Big Four = the largest 4 accounting firms: Ernst & Young, Deloitte & Touche, KPMG, and PriceWaterhouseCoopers.
Many students majoring in Accounting would like to be hired by one of the Big Four. Even graduates who don’t want to remain at one of the Big Four for an entire career see value in spending a few years at a Big Four firm as a résumé boost.