This page deals with slang terms for a Zombie apocalypse, in the heat of the moment it's easy to garble in horror at the situation and important messages are lost so easy terms are introduced by the military which are inevitably adopted and mutated by civilians.
In art, an underpainting is an initial layer of paint applied to a ground, which serves as a base for subsequent layers of paint. Underpaintings are often monochromatic and help to define colour values for later painting.
A self-leveling underlay is a cement-like product that can be pumped in liquid form onto the floor in order to create a level floor. Underlay is also the term for the material under roofing tiles; this roofing membrane is often made of rubber and is used to seal the roof and prevent leakage.