The Big Four refers to the four largest accounting firms in the world:

  1. Deloitte
  2. Ernst & Young (EY)
  3. KPMG
  4. PricewaterhouseCoopers (PwC)

These firms are multinational professional services networks that offer a wide range of services, including auditing, tax, consulting, and advisory services. They are known for their size, global reach, and expertise in various industries.