Wikipedia
In information security, de-perimeterisation is the removal of a boundary between an organisation and the outside world. De-perimeterisation is protecting an organization's systems and data on multiple levels by using a mixture of encryption, secure computer protocols, secure computer systems and data-level authentication, rather than the reliance of an organization on its network boundary to the Internet. Successful implementation of a de-perimeterised strategy within an organization implies that the perimeter, or outer security boundary, was removed.
Metaphorically, de-perimeterisation is similar to the historic dismantling of city walls to allow the free flow of goods and information. To achieve this there was a shift from city states to nation states and the creation of standing armies, so that city boundaries were extended to surround multiple cities.
De-perimeterisation was coined by Jon Measham, a former employee of the UK’s Royal Mail in a research paper, and subsequently used by the Jericho Forum of which the Royal Mail was a founding member.