It could also mean in a more general sense like an object being stretched while it is on top of another. Say a piece of elastic is on top of a surface and is being stretched. Another example could be a fabric laid on top of a table and being stretched to check its elasticity or to flatten it out.
If we think about it in a construction or building context, it could be a material like a tarp or a sheet of plastic that is on top of a structure and is being stretched to cover it properly, ensuring it is taut and in place. This is to prevent things like water from seeping in or for aesthetic reasons.