mainframe

Short definition from Wiktionary

Noun

1. 1
   A large, powerful computer able to manage very many simultaneous tasks and communicate with very many connected terminals; used by large, complex organizations (such as banks and supermarkets) where continuously sustained operation is vital.
2. 2
   A computer chassis that hosts and interconnects modules that perform various tasks.
3. 3
   The main frame of a vehicle etc., more commonly main frame.