Which is correct: on-premises or on-premise?

The correct term is "on-premises." This term refers to something located on a site or property, typically in the context of IT infrastructure, such as software or hardware that is hosted locally rather than in the cloud.  Additionally, some professionals prefer the abbreviation "on-prem" for casual contexts, which is widely accepted.

In contrast, "on-premise" is considered incorrect in this context. The word "premise" refers to a proposition or statement used as a basis for argument, which does not apply to physical locations. Therefore, using "on-premise" in place of "on-premises" is a common grammatical error that is often seen in marketing and tech discussions.