Line of Sight
Line of sight is a straight, unblocked path that indicates what you can see. Line of sight is like line of effect, except factors that limit normal vision, such as fog, darkness, and total concealment, can block line of sight. If you can’t see a target for any reason, you do not have line of sight to it, and thus you cannot use effects that require you to have line of sight. You cannot have line of sight that exceeds planetary range unless otherwise indicated.
Source
Core Rulebook pg. 271