What is the definition of dead sand?

Dead sand, in the aquarium business, refers to sand that is not populated with beneficial bacteria and other micro-organisms. Live sand contains such organisms which help aerate it when wet.

The second definition refers to sand that may be used as an "underneath course" for a finished layer of loose stones or gravel.

Dead Sand: A Lewis Cole Mystery is also a mystery fiction novel written by Brendan DuBois, featuring Lewis Cole who must find the mystery behind a girl found hanged and a group of prominent community members are marked for death.

Dead Sand is also a horror film currently in development.

Other possible definitions of "dead sand" also apply in the community answer below.

Dead sand does not exist. Sand is an abiotic substance of the earth that is neither dead nor alive. However "dead" sand could mean sand that is not subject to erosion of any kind, and thus just stays in one place for a very long time.

I think the second idea above is getting towards the correct answer. I've come across this term in drilled boreholes, and I assume it to mean that the sand does not flow, i.e. it has some degree of compactness or cementation.

The opposite to this (also seen in borehole logs) is 'live' sand, which I interpret as 'running sand' or 'piping sand', i.e. sand which is not bound together and tends to flow as soon as it is brought to the surface.