Concealment is a term mostly used while setting up a FFP (final firing position) or OP (overwatch position). These are locations the sniper will be spending a certain amount of time at.
As a sniper you will be needing a certain kind of cover. This is either physical cover like a wall, or ‘invisible’ cover. For example: Concealment or camouflage.
When we talk about camouflage we have to understand what it means first. A simple translation of this term is: making the visible, invisible (or at least less visible). Assuming you have some basic knowledge about this term, we’ll skip to the more advanced part.