A mainframe computer is a powerful and large computing system primarily used by organizations for bulk data processing, transaction processing, and critical applications. These computers can handle vast amounts of data and support numerous users simultaneously, making them essential for industries like banking, insurance, and government. Mainframes are known for their reliability, security, and scalability. They often run on specialized operating systems, such as z/OS, and can connect with various devices and networks. Despite the rise of smaller computers and cloud computing, mainframes remain vital for tasks that require high performance and data integrity.