Mainframes are powerful computers that are typically used in large organizations and businesses for handling complex and critical applications. There are several terms and phrases that are synonymous with mainframes, including "central processing units," "supercomputers," "large-scale computers," "enterprise servers," and "big iron." These terms all refer to the same powerful computing systems that are used for processing high volumes of data and running demanding applications. While mainframes may not be as commonly used today as they once were, they remain an important technology for businesses that rely on the processing power and stability of these systems for mission-critical applications.