According to Oxforddictionaries.com, a louvre is each of a set of angled slats or flat strips fixed or hung at regular intervals in a door, shutter, or screen to allow air or light to pass through. Thus, the vertical louvre is the part of a portable air conditioner that, as a set of vertical angled slats or flat strips, can be adjusted by angling the slats or strips to point either right or left in order to determine the left or right direction of air flow from the air conditioner into the desired space.