The Holoterminal is a technological fiction at this point, a form of workstation; but makes the stories far more fun. And in reality, there is reason to believe that such a facility will come to pass, bearing in mind that all things are interconnected including at subtle levels not normally experienced by the traditional five senses. I do not have a proposed mechanism for its functioning in these stories, unlike my concepts for transportation and space applications; but many people use devices based on "Radionics" that works for the operator; extrapolating from such functionality, one can come up with the general concept of a Holoterminal. In this saga the basic Holoterminal is invented by a KESTS technician's wife in the short story "Crisis On First KESTS."
So the Holoterminal in these stories is fantasized as a workstation where the user experiences oneness with anything to which attention is directed, that has an also fictitious substance called "holopaint" within or on its exterior. For example, all of the armature segments in the huge electric motor hoop of the KESTS, contain holopaint and thus are directly experiencable by anyone using a Holoterminal.