Cover
Cover is a mechanic, that reduces the hit-chance of a target shooting you from a specific direction, if you currently benefit from it.
Cover applies when you are behind an obstacle, you can still see over, but is not negligible enough to be considered too small for cover. Barrels and windows are a prime example of cover. When standing behind a window, or a barrel, enemies that shoot you only from the other side of it, will receive a 40% hit-chance penalty (50% with Barricade Tactician). Cover only benefits you from bullets coming from the direction of the cover, and will not help you if an enemy flanks you for example.
When deploying a weapon with , you also get a minor 10% bonus to cover (20% with Barricade Tactician). Unlike cover given by obstacles, this cover will work from all sides, even from behind.
You can see your cover-status to the immediate left of your Hit Points. A small Hex will denote, where you get cover from, and a number in the middle will indicate the strength.
Zmeja uses Cover in form of a barrel in this example, to get -40% Hit Chance from enemies that shoot from the right side. (Approximately from the orange area)