What is a data centre?

Simply speaking, a data centre is a facility used to house computer systems and associated components - such as telecommunications and storage systems - required to support a company’s business.  

A data centre generally includes redundant or backup power supplies, redundant data communications connections, environmental controls such as cooling, air conditioning, power monitoring and fire suppression plus various security initiatives.

Some companies may require a simple cage or rack of equipment, for others it could be a room housing a few or many cabinets, depending on the scale of their operation.  Large data centres are industrial scale operations using as much electricity as a small town.

More information can be found on Wikipedia and various other sites.