This means that an array is oriented parallel to the earth's surface, not towards the sun. This can happen in a couple of situations: from time to time the sky overhead is the brightest part of the sky, so generation is best at that angle of tilt, and also a flat tilt is good in high wind. When wind blows hard and a tracker solar system is in an exposed location, the force of the wind can damage the tracking mechanism. The tracking rack generally will have means of monitoring the wind speed such as an anemometer and automatically switches to a flat or tabletop orientation to reduce the purchase of the wind on the rack. Fixed racks generally have resistance to all but the most severe wind built into the design of the rack, in which case no tabletop action is necessary except in the most extreme weather events.