Yes - its the name of the paging device for the system. It allowed interleaved paging across multiple disk drives, so you could see and indirect look driver to multiple drives. It should be in section 4 of the BSD manual

On Fri, Apr 20, 2018 at 11:02 AM, Tim Bradshaw <tfb@tfeb.org> wrote:

I am sure I remember a machine which had this (which would have been running a BSD 4.2 port). Is my memory right, and what was it for (something related to swap?)?

It is stupidly hard to search for (or, alternatively, there are just no hits and the memory is false).

--tim