Mainframe - when it doubt use a Big Iron - the Awesome World of Things
Mainframe computers, commonly known as the Big Iron, are computers used primarily by large organizations for critical applications; bulk data processing, such as census, industry and consumer statistics, enterprise resource planning; and transaction processing. They are larger and have more processing power than any other class of computer. The term mainframe specifically refers to computers that can support thousands of applications and input/output devices to simultaneously serve thousands of users.
Read more about the mainframe over at LinkedIn here.