Sandbox - HeliosVirtualCockpit/Helios GitHub Wiki
In this wiki, a "Sandbox" refers to a Lua Sandbox, meaning a restricted execution environment for a Lua script.
Sandboxing with Lua 5.1 (the version used by DCS) is explained here: http://lua-users.org/wiki/SandBoxes
Sandboxing with the version of Lua used by Helios is comparable, but the syntax used is different. The concepts are the same.