On-premises or “on-prem” (and never “on-premise”) is the term used to describe traditional on-site IT delivery.  Typically used as a counterpoint to Cloud Computing, on-prem simply describes the way most Wintel services have been delivered since the early days of the PC boom.

Incorporating most forms of IT, on-prem can be used to widely describe not only Wintel environments but mainframe and midrange (including UNIX) as in a majority of cases, even when sited in datacentres owned and operated by third party service providers, the scaling, performance and licensing models of these environments don’t exhibit the defining characteristics of Cloud Computing.

There is an argument that mainframe computing is an early form of Cloud Computing and many of the concepts are similar, but rapid infrastructure scaling (as opposed to in-application scaling) and ubiquitous access are usually the limiting factors in mainframe environments clearly defining them as not being Cloud like.